What is a good argument for an intelligent student to not drop out sophomore year and get a GED to start college early?

If you're a good student and old enough to get your GED, is there any reason NOT to just drop out, get your GED and start college early instead of waiting through sophomore, junior and senior years of high school? You could almost have a bachelor's degree before your high school peers are even graduated from high school.

Aside from the social aspect, is there any good reason for a motivated student NOT to do this if they intend to go to a community college and transfer to a state school anyway?