Might be, it's been a while but from what I recall, they can only dedicate so much bandwidth to the channels, and have a cap that needs to be divided between the entire catalog of channels Bell (or Rogers) has, so while it's 4k, that doesn't mean there isn't significant compression,
With a streaming platform, I suspect there is more options available.
I'm not sure if SN and TSN are locked in at the quality set by the cable/Fibe that Bell and Rogers use, maybe the streaming app could go higher, but then it becomes a question of whether they made that backend investment or not,