I don't know but for some context, see the end of [1]. (It's not about Stripe specifically, but about why banks do this.) The whole article is useful background.

[1] https://bam.kalzumeus.com/archive/moving-money-international...

I figure they are betting that Ukraine will be sooner or later part of Russia.

or the limited partners of the private equity firms that invested in them are Russian oligarchs telling them what to do lol

This is pretty common (simply by the size of the investments), and Yuri Milner's DST Global was in some funding rounds so they probably have a big stake.

Yuri Milner is exhibit A of how the offshore feeders fund a bunch of US tech startups, mostly for the alpha, but that also comes with influence

https://www.theatlantic.com/international/archive/2017/11/yu...

So, sanctions result in cutting off Russia, investors result in cutting off Ukraine ha.