The ones who did in Crimea by voting to join Russia weren’t recognized internationally. In general though, if you’re in the middle of Ukraine and your family has lived there for centuries, even when Western backed fascists take over the country and start shelling you in the civil war, would you easily make the decision to leave for Russia instead of staying, trying to survive however you can? I think if people legitimately were invested in preserving the Ukrainian state’s territorial integrity, the press gangs wouldn’t be abducting people with vans, and the militias for the LPR and DPR wouldn’t have been able to recruit much of anyone at all.