I think, to be honest, it's just because this stuff really isn't google friendly. Or just... friendly,
at all. I've never seen that WorldCraft page before, and it's not for lack of trying.
this site got me through a lot of my early struggles with the entity system, but to be honest I've forgotten how I found it myself.
Another issue is that TB's docs aren't really noob friendly. I mean, they're great if you're a noob for TB, but not for quake. Anything you could possibly want to know about mangling a once-beautiful brush into a mess of non-integer vertex points and warped textures is contained within the bounds of the TB docs, but the only consideration given to the entity properties window is a guide to the UI and how to get around it.
Personally I don't think it should be the responsibility of the editor to provide documentation for this sort of thing. Especially not in TB's case, where the list of games it supports is quite wide and its capability to load custom entity definitions means that it can never cover every possible question.
There's no real solution here really; unless we start editing the top of the topic to include links to a F.A.Q. or tutorials like the one you linked, everyone is basically stuck in an endless cycle of answering the same old questions again and again...