It's usually geared powerlifters who have this issue; in fact, I'm not sure I've ever seen a raw powerlifter get the nosebleed / eyebleed thing.
The gear is very tight. If you're wearing properly sized gear, it can take 10-15 minutes to get into the briefs and suit, and that's having partners help you. That tight generates a huge amount of pressure, that's why it works - but yeah, smaller blood vessels will burst.
You ever use straps to lift? You know how your fingers turn purple from the increase blood pressure? A suit basically does the same thing to your head.