This is just due to lack of culture (80% of Bulgarians would stop reading here and would not read the explanation. Don't be one of them!). Most of the people who live in crowded Sofia didn't grow-up at a crowded place. Because even clogged Sofia was not crowded in the 60s and 70s. So the problem did not exist. Go to a cosy, not-crowded Bulgarian city and use the public transport there and you will see what I mean. It's ok not to take turns because there is enough space for everyone. And everyone is amazingly polite so they don't push you not because you are taking turns, but because they don't push you.
Suddenly, Sofia is crowded, no one is polite. There was never the moment when people could stop and think - ok, apparently we have to take turns, and it makes more sense to first get off/out of whatever and then to get on/in. It will take a lot of time to get this habit.
I'd be curious to find out how it happened in Germany because there it's impressive!