Precisely, Ukraine is a neighbor and many people in Russia have relatives in Ukraine and many Ukrainians have relatives in Russia. So there is no wonder why so many people from Russia want to help Ukrainians who are still leaning to Russia.
To help you understand a little better Ukraine and Russia is like Canada and the US. Ukraine like Canada is always in a shadow of its more powerful neighbor and always try to be more independent. It's just Canada is more developed than Ukraine, so it is not easy to convince people there to start a revolt against government.