vk is big in Russia (and some other parts) because they are proper Russian, in Russian and for Russians, and they are largely unmoderated, so you can easily find nice and nasty in the same place and also all the warez, porn (incl revenge and child) etc you will ever want. It's really the "wild east" there; I was pretty shocked when somebody started spamming child porn vk groups to one of the websites I moderate (and they were active weeks later still).
Then again, I was told by some Russian acquaintances that vk does not try to push American/European morals (like no nudity for America, no "hate speech"/gore for EU) and that really is how they explain it is so popular (then again, of course you wouldn't want to run an LGBT community on vk). Other folks from the West and Latin America found it useful too. E.g. I read that some German Nationalists/White Supremacist fringe groups moved to vk because it will not crack down on those groups, unlike Facebook.
But back to my point: if the EU really cracks down on facebook so that it is (forced to) stop(s) being available in the EU, then some new player from the EU might fill the gap and the network effect of friends and family may drive people to the EU version that anybody can use and away from the US version that EU cannot use and is a privacy nightmare anyway; so the effect may point in the opposite direction this time.
I know the likelihood of this happening is pretty low, but a lot less low now with the GDPR and the EU politicians' new found interest in facebook's business model.