[pvg]

Were you there?

Yes.

Isn't that exactly the action of post-Perestroika, now-democratic Bulgaria?

No. This was done under communist rule, as outlined in the Wikipedia page. Many Bulgarian ethnic Turks were able to return after the fall of communism as is mentioned there as well. A political party representing ethnic minority interests was one of the first formed after the end of communist rule. It remains significant part of the Bulgarian political landscape to this day - https://en.wikipedia.org/wiki/Movement_for_Rights_and_Freedo...

[thriftwy]

Why it didn't happen in 1949 then, or in 1959, or in 1969, or in 1979? What have changed?

I can see a clear link between perestroikas and ethnic cleansings, but perhaps you can reason that away.

[pvg]

It started in the 70s, which is in the Wikipedia page. Bulgaria did not meaningfully have 'perestroika' which you can google your way to. I don't think I have to reason anything away if you're simply unfamiliar with the history - you can just look it up or at a minimum, read the links we're talking about.