There's a few separate issues with using the official terms.
Inertia. People have been using Starter Pokemon and Effort Value for so long that changing them isn't going to happen for a lot of people. Wikis are better at this than most sites, because redirects are so powerful, but you can still expect folks to be complaining about this for literal years because we've got 2+ decades of habit to break.
Confusion. For example, Base Stats are now "species strengths", while Effort Values are now "Base Stats" and EV Yield is "Base Points". Expect a LOT of discussions to go off the rails while this happens because 2 users are using the same term to refer to 2 different things, links are now pointing to the wrong page, etc.
The official media DOESN'T USE THESE TERMS ANYWAYS. Partly because so much of the official stuff is in Japanese, partly because TPC/GF/Nintendo would like to hide the workings of the games from us, many if not most of these changes are things the EN community has never heard of before. If Nintendo would talk about things like EVs in-game, there'd be motivation for us to use their terms, but since they don't, "Nintendo calls EV's Base Stats" is a wacky trivia fact rather than something that should be at all relevant to us.
Inconsistency. It's already been pointed out that Official Pokemon DID use Starter for a while before changing their minds, and the official colors have always been a mess. If TPC decides to start calling EV Yields something different next gen, is Bulbapedia going to swap everything over again? Because that just makes the previous problems worse.
And the thing is, Bulbapedia is one of the big-name sites for this sort of information. Now that they've changed, every other site has to either change, or deal with an infinite wave of new users confused about why Species Strengths are Base Stats. Either it's a bunch of backend work to fix things like Showdown, or it's a bunch of moderator time dealing with noobs who now have one more information hurdle to get over before they can be part of the community. Neither is good, and Bulbapedia making this choice unilaterally forces every other site in the community to have the same discussion. (and that's before we consider THIRTY YEARS of old sites, printed guides, etc that are never going to be updated)