Ukraine hasn't been a part of Russia in well over 30 years. They don't "know" that. As Joester and others have pointed out, they are literally dying not to become a part of Russia.

From the link provided...

"In Ukraine, the language people speak cannot be equated with ethnic identity. A large representative study from 2013 examining the identity of Ukrainians living in various regions of the country found that the vast majority consider their ethnic identity as Ukrainian — the lone exception was in Crimea. More than 90 percent of people living in western and central Ukraine call themselves Ukrainian. But strong Ukrainian identification can be found also in predominantly Russian-speaking parts such as southern, eastern Ukraine and even Donbas — where 70 percent or more identify as Ukrainian."