They look so smart, sexy and hot and - Oh my, I could stare at them forever, why do they look so good in those things? I would totally date a dude like that if his personality maches up with mine too Lmao
And, as far as I can think, they look just very clean and as if they take care of themselves. THAT'S the main point of why I like seeing men in suits. Because not everybody walks around nicely dressed (counts also for women, the nice dress-thing).
It's quite appealing to see that you take care of yourself well, visually. What would make it perfect, is a good personality.^^
Most men look good in a well cut suit, because it's designed to emphasize a V taper. On top of that, it projects status.
Most (not all) women like a man in a well cut suit if he looks like he's going somewhere that calls for a suit.
If you are hanging out somewhere where the suit is inappropriate, you'll instead project that you're trying too hard to look important, which makes you seem like a loser, no matter how nice your v-taper is.
A well-cut tuxedo looks nice in the evening, but out of place at the beach. That's an extreme case, but the principle holds - dress well but appropriately.