It's a whole raft of stuff that is not what it once was. Hollie Davis posted an article in MAD this month about this phenomenon, it's much deeper than antique collecting she argues, golf, fishing, knitting, camping, boating, etc, etc, etc are all down in participation, and Americans' hobbies/leisure time are changing fundamentally in different ways.
I think she's right, the old hobbies are just not what people are spending their time on these days, all across the board.