Some of the replies are kind of funny. The caliber of SportsNet's coverage is irrelevant to the NHL, and there isn't any *giving* the rights to TSN or the CBC. This was a bidding process, not an audition.
Rogers thinks it can make money off the NHL, either with its own broadcasts, branching out into other terrestrial radio and online media types, and/or selling some of those rights to other entities. So it bid a higher number than anyone else. The NHL likes money. If Bell had wanted to bid more, the NHL would have liked TSN too (or instead). Same with Amazon (though I suspect they'll get some of the rights via Rogers, in the end).
Growth is literally Gary's job, and so this is a home run for Bettman. It'll be the last substantive achievement he racks up before his retirement in the next couple of years. Then we'll have 20 years of Bill Daly doing the same.