If you look at https://en.wikipedia.org/wiki/Corruption_Perceptions_Index you can also notice how post-soviet countries that keep close ties with russia also still rank high on that. I wonder how much of that is from same kind of people keeping power, or russian influence.
The Wikipedia article is a little bit light on the bribery aspect, but there seems to have been considerable efforts made before 2012. https://en.m.wikipedia.org/wiki/Corruption_in_Poland