[andolanra]

I'm not sure what "cool advanced projects" you're thinking of, but to my recollection, there was very little in the way of finished work created with the original Blender Game Engine. There were two game efforts associated with the Open Movie Projects: Yo Frankie! (associated with Big Buck Bunny) and Sintel The Game (associated with Sintel.) The former had something like a proper release, but the latter only ever got a few alpha releases before being abandoned: neither was terribly impressive except inasmuch as a demo of the technology, and to my recollection, neither inspired much hype. (The Wikipedia page for Yo Frankie! says dryly, "The game was noted by the gaming press," without any further elaboration, which does not speak to massive amounts of excitement or hype.)

Since then, aside from some interesting bits of work that didn't actually make shipping games easier, the engine really languished. My understanding is that a big part of the reason the engine was removed was that it made work on other parts of Blender more difficult, and that dispensing with the (little-used) engine in favor of the (increasingly popular) modeling tool was clearly a net benefit to being able to develop Blender, especially since the mantle of "open source game engine" had been taken up by other competent projects like Godot.

So yes, they may have at some point aspired to becoming a "mainstream game engine", but there's more to that effort than just aspirations and demos. (And at the same time, the fact that the BGE faltered doesn't mean that other open source game engine efforts would necessarily face the same fate.)

It's probably also worth saying that people have forked the game engine and you can still use it: the forked version is called UPBGE, and there are people out there trying to make it work. By and large, though, the Blender project seems to point people at projects like Godot, with the idea that a focused game engine is probably better suited to modern games than something that strapped a game engine onto a piece of modeling software.