It is not just US, also in Europe it seems like the hitchhiking is dead. 15 years ago when I was criss crossing Europe many times hitchhiking, sleeping in hostels but usually just in the ditch next to the road or field nearby. I used to meet tons of hitchhikers almost anywhere you go.
Today I am not hitchhiking anymore, but I am happy to give a ride to anybody flagging finger. For past three years that happens only once and even those two people were doing it just because of some hitchhiking competition.