So let me get this straight. You just want them to resub rather than banning players that are ruining the game? Sorry if I'm misunderstanding but to me that just seems like all blizzard cares about is cash flow.
Sorry, let me try to explain more clearly:
Take your average botter. Let's call him... Jim. Jim is an awful person who uses various scripts and/or third party programs to give himself an unfair advantage against other players. We don't like Jim. One day, Jim gets caught, and Blizzard takes action against his account.
Now say, hypothetically, that Jim's account gets permanently closed. Everything he had on that account is now gone forever, and he has no way of getting it back. Now, many players in this case would (and do) just stop playing, but not Jim. Jim decides he still wants to play World of Warcraft, so he buys a new account and starts over fresh. And since Jim's now starting from scratch, he decides he doesn't have much to lose, so he fires up his scripts and third party programs again.
Net result: Jim is still at it. If and when he gets caught again, he just buys another account, and continues to be an awful person.
However, if Jim only gets a temporary suspension, he knows he's getting his account back, so starting over from scratch sounds much less appealing. Jim likes his characters and wants to keep them, so he decides to just wait the suspension out. Once it ends, he really doesn't want to go through that whole ordeal again, so he decides not to risk botting again.
Net result: Jim is a decent guy who made some mistakes and learned from them. We're actually pretty okay with Jim now.
I'm obviously painting a rosy picture here (not everyone responds this way), but I'm just trying to illustrate why suspending accounts tends to result in fewer cheaters long-term than permabanning. Like I said, there's some really interesting psychological shenanigans involved (which are a bit above me, I'm afraid). That's my understanding of how all this works, though.
(Also, apologies to everyone named Jim who is not a filthy cheater. I'm sure you're all lovely.)