There are 2 kinds of people in this world--those who gawk at the health club, and those who admit it.
Seriously, everyone looks, even those people who are protesting. Shakespeare had it right. "The lady doth protest too much, methinks" (Hamlet). A beautiful body is a powerful motivator. Looking isn't a bad thing. Staring and truly gawking is rude, of course, but looking isn't bad at all.
Seeing someone who has a body you admire can give you the gumption to make that extra mile, or to do that last set. It's a palpable goal that you can physically see. Seeing someone of the opposite sex can make you think--"gee, if I can get in shape, I have a better shot at dating someone like that." Sure, it's a bit mercenary, but . . . whatever it takes to get you through your workout.
It can also take your mind off the drudgery of your workout.
EVERYONE looks. Just not everyone will admit it. Plus, "gawking" is a lot stronger than looking--people get defensive, lol.