Thom Browne set up shop in New York in 2004. With this he began creating a different fashion for men, one that looked back at an older style (roughly from the late 1950s/early 1960s) and mixed it with a bold new look.
Why wear something that is too short and looks incredibly uncomfortable? Why look like a kid who doesn't know how to dress himself (while paying crazy prices to do so)?
'Cause it's the 'fashion' right now, to look dressy enough for work but casual enough for a good time afterward. Frankly, I find it quite ungainly and childish. But each to his own.
Style and fashion are two totally different ideas. Style is classic and lasts forever, like a vintage fedora, a nicely fitted suit or...socks. Fashion takes aspects from stylish clothing and messes with them, turning them into Frankenfashion that goes against the grain. Fashions last from fashion season to fashion season, until something 'new' and more 'fashionable' comes along. But style, style lasts.
Ugh. I'll take the overcoat but everything else is bad. Suit shorts? Well, at least he's a fan of sock garters, that is when he's wearing socks.
Here's a "New York Times" article about Thom Browne and his ilk.