That’s not the point. If you paid 10 bucks a month for a long time, but Blizzard could squeeze out another 10 bucks a month from you by offering a sweet deal, then of course they will seek to do that.
If you have 50 bucks worth of disposable income, then it’s Blizzard’s goal to try and get as much of those money as possible. Because if they don’t, then someone else will. That’s called competition.