I feel like there's a lot of confusion, so not sure if anyone can clear up mine, but I'm really struggling to see a significance of this.

Obviously, like all ignorant people do, I am going to oversimplify things here. But still, to me, the "platonic idea" of Anki seems a dead simple thing. All what I care about when using Anki is what's on the 2 sides of a Card, a question + answer, which can only be some visual image (possibly encoded as text, possibly just JPEG, I really don't care as long as it fits in my mobile device memory) + optional sound. That's really it. If it should be bi-directional or uni-directional card is a detail of how the deck is generated/encoded, and the spaced repetition algorithm is a detail of the app that I use to study (so, usually AnkiDroid, I imagine — an unaffiliated 3rd party; who even uses desktop apps nowadays?).

So, I imagine there can exist (and do exist) some minor additional features, like an ability to require a typed answer for a card, but it seems pretty minor, and I really don't see a lot of room for the app to evolve.

So, ultimately people need only a common .apkg format, which exists and is relatively simple (although I suppose it could've been even simplier), and a place like AnkiWeb, where people can share their decks, so Spanish top-2000 or basic integrals deck isn't re-invented over and over again. It's a pity that AnkiWeb isn't more open and will be even less open from now on, but as long as someone is willing to just host it (which is ultimately just paying for downloads traffic) it's easy to replicate, so no super-valuable IP here.

Of course, a primary use-case for Anki is a tool to make decks, but you could really do with pretty simple python script + YAML/JSON/CSV/whatever metadata file to convert it to AnkiDroid-compatible .apkg file.

So, basically, who cares? What is to "own" there?

IMO, the add-on value is the repository of decks that exist (and may or may not be free).

So an app-store of sorts.

As others have said, there are some provisions in place that make it allegedly harder to do a hard landgrab and keep people from freely sharing decks, to to me, even if it were so, I would not be too concerned.

In my opinion, the very act of creating one's deck is a key part of the learning. Maybe it's different for larning vocabulary, but as you said, it will be very hard to make those hard to share.

Learning a deck generated by someone else has never been as effective with me, so I think it's a false sense of time saving to use those.