The important parts are paint and maintenance.

Give a commie block a fresh coat of paint every decade or so and they can look good (though I just don't like flat roofs. But that's personal taste.)

But while a somewhat run down european style house can still have some charme for longer (guess I'm biased here) a run down commie block in gray and with cracks in the facade will quickly start to look depressing.

And as they are often chosen for cost reasons inside capitalistic environments, they are often neglected.

So, the problem is not commie blocks, but how they are maintained. And as often we tend to search for the extreme examples if we (dis)like something.