Question about religion in Eastern Europe?

The percentage of people who identify as Christian is very high(over 80%) in all Eastern European countries except for The Czech Republic(just 29.3% Christian) and Estonia(just 24% christian) which are the countries with the most non-religious people in the world. Why is that? What caused this huge difference between the two and the rest of Eastern Europe? Could it be be because of Estonia's proximity to very liberal Scandinavia and Czech Republic's proximity to liberal Germany