Not sure about the situation in Czechia but in Spain (where I live) I'd say most of it is caused by the fact that jobs have moved to the big cities to the point where there's nothing left to do in small/mid-sized towns. Personally I blame shopping centres (which have destroyed most small stores in every town they've settled in, and don't require as many active people) and cheap production in Eastern Europe and China (which has destroyed the secondary sector).