Not many tracks could hold 75,000 now though, but I get your point!
It's not only down to those things though, is it?
Much wider choice of entertainment (be that entertainment be cheaper or not) is another major factor, as is, most probably, the cost of getting to and in to a track and a whole raft of other problems (many to each individual track, i.e., one tracks 'problem' could be different to another tracks 'problem').