I don't know that Mosport knew this was coming. I know (or I heard) last fall that they were looking at options for the oval including developing and expanding it, turning it in to a dirt oval or closing it. The sad fact is that asphalt tracks today, all of them, are experiencing low car counts and low spectator counts. The dirt tracks, e.g., Oshweken, Brighton, etc. seem to be doing much better.
Everything at Mosport now is about the bottom line. Ovals don't make much money. Driver development tracks do.
I also don't agree that it is the promoters that keep driving up the cost of race cars. Often it is a few drivers who want to use some new and expensive gadget to go faster.

If race tracks do not freeze rules for at least 3 years at a time they will die a slow death.  just my opinion  but its true