Everybody wants to be as good as you can be.
Which can mean, stronger, faster, more athletic, prettier etc
Some dudes go the extremes and use surgery (which rarely improves), but most train something to become better than they originally were.
I never started training in the gym for looks, i was training Martial Arts at the time and wanted to be able to lift/toss heavier and punch stronger (i was young)
I wanted to become stronger and complement the MA-training.
After a while training in the gym, it changed. I was training in the gym more , and less training Martial Arts until a period where i only trained in the gym and no more MA.
I appreciated the strength-changes, but now i also noticed some body changes / aesthetic changes (i saw how my arms got bigger, chest got bigger etc) and was bitten by the iron-bug and enjoyed it more than punching, kicking etc
It ruined my Martial Arts-aspirations for sure but i gained something else.