I haven't seen any of these tools doing anything that anki doesn't — why not contribute to it instead?
However it probably is worth considering an import of Anki cards in the future. For now though, I'm focused on cards with answers you'd only know.
If anything new Anki UI project would be more impressive and clearly in demand compared to yet another flash card web app.
For the same reason that your area likely has more than 1 pizza restaurant. Other people want to take a stab at their own vision of a thing and that's awesome. Personally, I find Anki to be pretty uninviting to the general public.
Fluent-Forever.com is an example of an application of spaced time learning applied specifically to languages and their app is pretty great.
We may disagree philosophically, and that's ok, but I tend not to buy into the perspective that if X already exists and Y is like X then Y should not exist.
I don't mean to be harsh or mean but OP is treating this as a product rather than a hobby projects with producthunt submissions etc. when in reality it's a barebones clone of a standard application that already exists.
Open communities benefit from numbers. Another developer to Anki even if you'd just wrap around nice web ui around it would be significantly more efficient and valuable then reimplementing the same spaced learning logic and starting everything from 0.
The whole point of Anki is to standardize this field - it's libre software made for the medium not for profit.
It's also a very old project where it's hard to enact change that you might want. So if you have a different vision, there's no way to realistically implement that.
But it's not. Just look at the source code for card[1]. It's modern, fully type hinted python3 code, you don't even need to know python to understand big chunk of it.
1 - https://github.com/ankitects/anki/blob/master/pylib/anki/car...
Also, the web client is very bare-bones, unfortunately.