Because popularity isn't directly related to quality?
I find Rewrite (VN) to be bloody amazing and remember just about everything about it (which is also sad in a way, no way to relive that first playthrough), but it's not exactly popular, right? When I say Kagari, you say LWA, when I say Kotori, you say Date A Live, because they're popular. Yet I can't for the life of me remember whatever the fuck happened in Date A Live, other than the quickly forgotten premise of "uhhh his choices aren't really made by him", because I found DAL from a recommendation from NouCome.
tl;dr: they're overhyped