I might be wrong but I think that's essentially urbanization - when I lived in Poland 20+ years ago, a lot of people still lived on farms and ate beets and stuff. My very own grandfather had his farm torn down and an apartment building built in its place 10 years ago or so - got a free apartment for life out of it.
I think the stat was.. 50% or something close to it of the country was still rural. I guess that's changing rather quickly, with all that EU cash and the economy doing so well (relatively speaking) and all.