"Tell me you don’t know much about gymnastics without telling me you don’t know much about gymnastics"
Robinhood, you beat me to it!
Elite gymnasts train for over 20 hours a week (often considerably more). As a result, quite strong sub cultures develop, including fashions. There are trends not only in training and competition gear, but in hair styles and accessories. FIG (the world governing body) have quite broad rules based on clothing being tight enough so the line of the body can clearly be seen (e.g shoulders, hips and toes form a straight line) and modest (e.g leotards not being g-strings). The rest typically is driven by gymnasts and trends they start. A relatively new trend, taken up in some countries and not others (yet, I expect they'll follow), after presenting, instead of walking to your starting position on the floor, to do a mini dance routine to get in to position. This trend was started by gymnasts not coaches or FIG.
Gym training is pretty gruelling with lots of strength, stamina and flexibility work. Then there are lots of reps (drills) - doing the same sets of movements over and over. Once you have a new routine, you practice this over and over.
Competition is the fun bit, the bit where all this training comes together. The goals is to perform and entertain. Gymnasts want to wow the audience - it is what they have worked for. If they didn't want to do this, they would not commit to all that it takes to get into an elite squad.
Gymnasts could choose sports that are simply about being the fastest or strongest. They could choose sports that involve team work, but they have chosen a sport with a strong artistic component (the clue is in the name!). It's ludicrous to suggest they have to endure this element of the sport.