Bell Media's businss reasons for showing NFL on CTV is that they get to simsub the signal - so almost the entire country - is getting ads for which Bell Media is getting paid for. They capture as many NFL viewers as possible to maximize their ad revenues.
For example if 1.5 million people are going to watch football at 1:00PM on Sunday - let's say 750,000 watching NFL, 750,000 watching CFL - Bell media will capture all 750,000 CFL viewers. But if the NFL games is on TSN Bell Media would lose out on the ad revenue from everybody actually watching the NFL games on the originating American station instead of on TSN - and that can be a pretty substantial number.
A couple of years ago when there were four NFL playoff games one weekend ond one of the four was on TSN and the other 3 on CTV - Bell Media's ratings for the game on TSN were over 400,000 less than the average of the three games on CTV - which is a good indicator of how many viewers they lose when the simsub is not in effect.
It is all about maximizing advertisng dollars for Bell Media. There is a reason CTV doesn't officially announce what NFL games are being shown where across the counry each week until Wednesday. That is done after the American networks release their national broadcast maps - for which games are being shown where. So for example here in Southern Ontario if the NFL American broadcasts maps released on Wednesday morning shows that at 1:00PM the Buffalo FOX station is showing a Giants - Eagles game for example - you can bet that later that day CTV will announce that either CTV Toronto or CTV2 in this region will also show that game to be able to simsub the signal and capture all viewers.
Having said all that it still would be nice to at least get the Grey Cup on an over the air station to maximize ratings. Heck - they showed the Santa Claus Parade here in Southern Ontario yesterday at 4:30PM on CTV Toronto instead of an NFL late game. Why not do something similar for the Grey Cup?