Natural beauty's great, but some people don't seem to understand that all girls aren't naturally beautiful and some would like to be considered attractive nonetheless. Makeup helps us achieve that. I wear a lot of eye makeup and I get a lot of comments about it, but people are going to say what they're going to say; you know what looks best on you, and they don't.
theyre jealous comvbined with insecure and don't want other girls to get ahead of them
In my experiences, a lot of the girls who put down other females for "coating" themselves in makeup usually aren't the most attractive and could probably benefit from some mascara themselves.
Also, I think it may have something to do with the fact that these girls always hear guys say they like "natural" girls etc, so by not wearing makeup they may get a feeling of superiority, almost like, "guys like me better because I'm natural and that's what they prefer" etc... kind of like girls with big boobs who feel superior to those who are small chested because many guys prefer large boobs.