Now that I think of it, I'm betting part of the reason A Bug's Life is pretty much forgotten is because I think around the same time is when DreamWorks came out with Antz, which, as DreamWorks animated movies used to be, was darker and edgier than A Bug's Life (and also had a more A-List cast of voice actors).
Speaking of which, when did DreamWorks decide to tone down their animated movies? I was thinking about it the other day, the first Shrek movie had more swearing, more suggestive humor, more... uh...anatomically... uh... well it almost seems like all of the female characters seemed rather top-heavy, almost all of which has disappeared from the following Shrek movies; likewise, most other DW movies have been rather toned down as well... SharkTale is an exception, obviously, considering it was a parody of adult movies anyway.