If the quality of 1040 was so much better than Sportsnet radio, you'd have to think Rogers will be trying to grab as many of the old TSN people as possible. Of course money might be an issue as well.
If you look at the ratings, it makes sense why they made this decision (here's the most-recent numbers from the end of August through November):
https://assets.numeris.ca/Downloads/...plineRadio.pdf
CKST is TSN, CISL is Sportsnet. TSN was the 4th-lowest rated station in the market. Sportsnet is one of the three stations with worse numbers, but that doesn't mean TSN's numbers were good.
Even if everyone who listened to TSN switches to Sportsnet, Bell can still probably get similar numbers for a significantly lower cost with whatever new format the station switches to.