The truly funny thing is, we know that people overwhelmingly used homebrew campaign settings. WOTC's come out and stated as such.
Therefore, the past 30 years of D&D history didn't mean squat to most people. Most gamers wouldn't know an aasimar if it came up and bit them on the petoot. If people are, by and large, playing in their own worlds, then what possible difference could it make to jettison core "canon"? Which wasn't really canon because it only applied in very limited circumstances. The Tiefling background, for example, only came into the picture if you played Planescape, a setting that's been OUT OF PRINT for over a decade.
Anyone who came to D&D through 3e probably has zero idea and zero interest in that "thirty years of history" baggage. Why would they? It doesn't apply to their game. It doesn't make any difference to their table. So, the only reason to keep it is to keep a small core of fans happy. The majority of fans couldn't care less.