On their forum they put the success of Leeds support down to the YUK (Yorkshire Ultras Kollective) who have come up with a load of new songs. It took a while for the new songs to catch on but they persisted with it and now you get a great atmosphere at Leeds games with everyone singing together.
Standard stuff. Leeds numbers are impressive because they were once a very big club. When we were in Div 3 they were winning major trophies. Gallows humour on a losing away day. If I was 30 years younger and/or drunker I'd have been singing "You're too shit for us to care!".