Requiring ID prevents scalping because you have to be the person who paid for the ticket in order to use it. IIRC my last TicketMaster ticket was transferable

Requiring ID prevents scalping because you have to be the person who paid for the ticket in order to use it. IIRC my last TicketMaster ticket was transferable - there was a webpage where I could change the name. But presumably if one credit card/IP address transferred the majority of its tickets, you could say with some confidence that that person is a scalper and shut them down. The limit on purchases is reasonably effective, though.