It's a bit arbitrary ... it's kind of random, but after being an AboutUs community contributor for a while folks often get AwardedACaricature. Since the caricatures are made from portraits, it's safe to assume that all of these folks have uploaded a relatively high resolution portrait (at least 500px on a side). Not everyone who is awarded a caricature chooses to keep the badge on their PersonalPage, so some folks who have been awarded a caricature don't show up here.
Caricature awards aren't meant to be fair ... they're meant to be fun! So don't sweat it and have fun :-)