But that hasn't really turned out to be the case, has it? 4E fractured D&D fandom, sure, but many people who bought many 3E books have started in again with 4E books. Right? Also, I'm relatively certain that if 4E had been an evolution of 3E -- fixing its problems, introducing some new systems -- I'd still be buying.
I think here is one major point - the WotC designers and many 4E players probably thinks the changes are an evolution of 3E.
But you don't. Could Wotc or its designers predicted this and find a different route? (And both is required - if they knew the "Jeff Wilders" of this world will be lost to us but couldn't come up with a way to keep them, this couldn't change their course of action.)
WotC put out "test samples" of 4E - did you enjoy the Bo9S? Did you like the Warlock or the Reserve Feats? Did you look into Star Wars Saga Edition? How did you feel about the skill system?
I suppose WotC put these out and saw that people liked this. And so they eventually they felt safer with the system ideas they had in mind.
But each of these individual aspects might have been a subset of what you didn't like in WotC material. Maybe you bought Bo9S, but found it one of WotC weaker products. Maybe you didn't like Reserve Feats or the idea of "always available magic". But you still bought these products because before you personally saw them, you wouldn't have guessed that these rules weren't to your liking - or because other aspects were.
I recognize that it's very subjective, but I honestly feel that it's not that I decided to stop buying WotC products, but rather that WotC decided to stop making products that I want to buy.
I don't know how much this was a conscious decision on WotC, but I suppose they decided to create products that turn out not to appeal to you.
It wasn't a decision of "Let's no longer appeal to gamer type X" but more "Let's appeal to gamer type Y" or "the market is changing to more gamers of type Y". If we were to create Venn diagrams, there is an overlap between "Gamers of Type X" and "Gamers of Type Y" and 3E covered a little of both (but not all), and now 4E covers a little more of Y and less of X.
I suppose WotC hope is that the extra part of Y is larger then the part of X that got lost...