Because another show has the theater booked for Fall and if they did not announce closing as early as they did they probably wouldn't be making what they are making. Sure, they'd have their summer tourists as usual stopping by, but these numbers are IMPRESSIVE. I wouldn't be surprised if there's some life after Broadway after all, in whatever form that may be.
My question is "how much of the increase in Mamma Mia's sales is due to it closing and how much is due to it being summer so bookings are up?" I appreciate that it will be benefitting from last few weeks panic sales for punters to see it one last time but actually, it's been weeks now. I wonder why the producers did not keep it going through the summer and then announce its closure in, what I believe are the quieter times.