There are many potential reasons, but I am going to keep it simple and give you just two. The first and most common reason people suffer from underactive glutes or “glute amnesia” is due to lifestyle. Even when people train hard every day, if they spend the majority of the remainder of the day sitting down, then they are simply not using their glutes. And remember the old saying - if you don’t use it, you lose it. Unfortunately, this is just what happens with your glutes.
Polyethylene glycol is a non-toxic, water-soluble polymer that is capable of enhancing the absorption of creatine and various other substances [66]. Polyethylene glycol can be bound with CM to form polyethylene glycosylated creatine. One study [67] found that 5 g/d for 28 days of polyethylene glycosylated creatine was capable of increasing 1RM bench press in 22 untrained young men but not for lower body strength or muscular power. Body weight also did not significantly change in the creatine group which may be of particular interest to athletes in weight categories that require upper body strength. Herda et al [68] analyzed the effects of 5 g of CM and two smaller doses of polyethylene glycosylated creatine (containing 1.25 g and 2.5 g of creatine) administered over 30 days on muscular strength, endurance, and power output in fifty-eight healthy men. CM produced a significantly greater improvement in mean power and body weight meanwhile both CM and polyethylene glycosylated form showed a significantly (p < 0.05) greater improvement for strength when compared with control group. These strength increases were similar even though the dose of creatine in the polyethylene glycosylated creatine groups was up to 75% less than that of CM. These results seem to indicate that the addition of polyethylene glycol could increase the absorption efficiency of creatine but further research is needed before a definitive recommendation can be reached.
In competitive bodybuilding, bodybuilders aspire to develop and maintain an aesthetically pleasing body and balanced physique.[16][17] In prejudging, competitors do a series of mandatory poses: the front lat spread, rear lat spread, front double biceps, back double biceps, side chest, side triceps, Most Muscular (men only), abdominals and thighs. Each competitor also performs a personal choregraphed routine to display their physique. A posedown is usually held at the end of a posing round, while judges are finishing their scoring. Bodybuilders usually spend a lot of time practising their posing in front of mirrors or under the guidance of their coach.
Your glutes serve as the main mover and power output to most of your major and accessory lifts—squat, deadlift, kettbell swings, box jumps—so the more you develop and stimulate your gluteal muscles, the more you’re able to maximize control, strength, and stability. (It doesn’t hurt that women love watching you do leg and glute work in the gym, either.)

If you’re looking to put on extra muscle mass and build strength, there are a few things that need to occur. The first of these, even though it may seem obvious, is that you will need to have an exercise routine. To stimulate maximum muscle growth, you’ll need to challenge yourself in the gym, forcing your muscles to adapt to heavier workloads by increasing in size and strength.
Some of these medications that can harm the kidneys include cyclosporine (Neoral, Sandimmune); aminoglycosides including amikacin (Amikin), gentamicin (Garamycin, Gentak, others), and tobramycin (Nebcin, others); nonsteroidal anti-inflammatory drugs (NSAIDs) including ibuprofen (Advil, Motrin, Nuprin, others), indomethacin (Indocin), naproxen (Aleve, Anaprox, Naprelan, Naprosyn), piroxicam (Feldene); and numerous others. 

If you'’re looking to add muscle mass to your frame, hitting the weights hard is a given. Quality time in the gym begins a cascade of changes that will stimulate your muscles to grow bigger in response to the challenges you throw their way. It'’s tempting to think that'’s all it takes to add muscle to your body. After all, you can actually feel your biceps growing after an intense set of curls. 

As blood levels of testosterone increase, this feeds back to suppress the production of gonadotrophin-releasing hormone from the hypothalamus which, in turn, suppresses production of luteinising hormone by the pituitary gland. Levels of testosterone begin to fall as a result, so negative feedback decreases and the hypothalamus resumes secretion of gonadotrophin-releasing hormone. 
In vitro studies on endothelial cells have noted that the benefits of creatine against atherosclerosis (via immune cell adhesion to the endothelial cell) are blocked with the pharmaceutical ZM241385, a high affintiy adenosine A2A receptor antagonist.[316] This particular receptor subset (A2A rather than other adenosine receptors) and its inhibition are similar to caffeine,[589] suggesting that caffeine may have an inhibitory effect on this mechanism of creatine.
After the ingestion of 5g creatine in otherwise healthy humans, serum levels of creatine were elevated from fasting levels (50-100µM) to 600-800µM within one hour after consumption.[135] The receptor follows Michaelis-Menten kinetics with a Vmax obtained at concentrations higher than 0.3-0.4mmol/L,[136] with prolonged serum concentrations above this amount exerting most of its saturation within two days.[137]

Volek, J. S., Ratamess, N. A., Rubin, M. R., Gomez, A. L., French, D. N., McGuigan, M. M., Scheett, T. P., Sharman, M. J., Hakkinen, K., and Kraemer, W. J. The effects of creatine supplementation on muscular performance and body composition responses to short-term resistance training overreaching. Eur.J.Appl.Physiol 2004;91(5-6):628-637. View abstract.

I’m going to cover this in detail in a bit, but for right now, just know this: it’s VERY possible (and common) to gain weight fast in the hopes of gaining muscle fast. The problem, however, is that the majority of the “weight” a person in this scenario will end up gaining will be body fat rather than muscle mass. This is something that needs to be avoided at all costs, and I’ll show you how a little later.
While there are many reasons why an individual might have weak glute muscles, one of the main causes is that many of us are living increasingly sedentary lifestyles. Many jobs now involve people sitting down for a big part of their day, or after a long day of work we go home and sit on the couch; this means that the gluteus muscles can become dormant more than they should be. Another reason why someone might have weak glutes could be because of poor form and generally over-relying on other muscles during everyday movements, which contributes further to the muscles remaining inactive. 
Sandow was so successful at flexing and posing his physique that he later created several businesses around his fame, and was among the first to market products branded with his name. He was credited with inventing and selling the first exercise equipment for the masses: machined dumbbells, spring pulleys, and tension bands. Even his image was sold by the thousands in "cabinet cards" and other prints. Sandow was a perfect "Gracilian", a standard of ideal body proportions close to those of ancient Greek and Roman statues. Men's physiques were then judged by how closely they matched these proportions.