While I agree, this position has a number of logistical problems.
First, there's the issue of actually obtaining the books. You can make do with just one, assuming you're not playing online, but it's kinda nice when everyone has their own copy. If you are playing online, well, good luck.
Second, each of these games tend to represent a significant investment of time. I once thought about buying the Game of Thrones RPG, but one look at the table of contents had me reconsidering that notion. People spend a lot of time learning to play these games and becoming competent enough to go play without interruption takes even more time. Here there is a case to be made for rules-light games, but some don't find those quite as satisfying.
This is an expensive pastime, in terms of both time and money. Metaphorically speaking, having a common language is not without benefits. It'd be nice if that common language were a little better designed, but that's the baggage it carries.