Have you ever looked at the Mediawiki code base? Last time I skimmed a bit, a few years ago, it was an utterly horrible mess of spaghetti PHP. Just finding developers capable of doing this would be a big challenge. The Wikimedia Foundation has a lot less resources than you might imagine, considering the reach of its projects, and there are an awful lot of other funding priorities (not to mention other code priorities). They’re doing the best they can, but making sweeping changes to the code base is a lot harder than it looks.
> I think there are powerful members of the community who want to keep it somewhat insular and closed off as a defense mechanism.
Do you have any evidence for that? As conspiracy theories go, this one seems pretty weak to me. I can’t think of another organization of comparable size which is as welcoming and open to involvement and contribution from ordinary community members, at all levels of decision making. Almost the entire management and operation of Wikipedia and the Wikimedia Foundation is carried out in public, nearly all of the parties involved are volunteers (with a quite small number of full time staff keeping infrastructure running, handling legal issues, and so on), and many many decisions are made collectively, by consensus.
It’s easy to hate on anything, as a disinterested outsider, without making any real attempt to understand the internal processes involved, but organizing millions of people is a highly non-trivial job, and I think the Wikimedia community has done pretty admirably, all things considered.