Why was it so hard for some of the Eastern Europe countries to change to capitalism and not the other countries?

The transfer from an economy dominated by central planning to an economy dominated more by market mechanisms was difficult for most of the Eastern Block countries. Generally speaking the closer the country was to the affluent West the better off the country did since foreign investment was an important component in the transformation. Poland allowed quite a bit of private ownership. The former Soviet Union had a particuarly difficult time because not only did it go through an economic transformation; the country also, quite literally, fell apart, so there was also a political transformation as well.