The same reason why a park buy an old SLC like Michigan's Adventure, or a Boomerang like Carowinds. It's all relative to the park's specific needs. Some parks do better with specific types of rides than others. Does that make sense?
I agree with you, there are better types of designs out there, but they're not always the best option. Sadly.
MA and Carowinds didn't "buy" the rides, they were moved from another Cedar Fair park (GL). Cedar Fair simply wanted to get the most out of the closed property and move the rides that had some appeal as "new" attractions.
A stand-up makes no sense to me in a lot of ways. There hasn't been one built in a decade, they are terrible rides (best one I've been on is Georgia Scorcher and it wasn't very good at all), and as far as I know B&M started telling everyone to NOT buy them ages ago... A sit down makes a lot more sense.
Carowinds and MA may not have "brought" the ride but someone has to fit the bill for dismantling, relocation, and reconstruction. I imagine when you add that plus paint, and the new train(s), it adds up to only a small discount from what a new one would have costed.