In the U.S., a lot of it is dance-oriented. Pianos are not portable enough, and a lot of dances were house dances that didn't have a lot of extra room and a lot of people didn't have the money for a piano. They are relatively common, though, as back-up in Midwestern old-time music (often in place of a stand-up bass).

And of course you hear of a lot of musicians who learned piano either in church or in whorehouses. I guess those were the two entities that did have the money and space for a piano.