SF Great Adventure in NJ actually has a few indoor rides:
Skull Mountain (family coaster)
Justice League (shooter)
Dark Knight (wild mouse)
Houdini's Great Escape (spinning illusion dark ride) [open peak times]
And they have no effect on how the park functions. All last week, we had constant rain storms and the park closed early (or didn't open at all) every operating day. You really need at least 50% of your rides to be indoor to make a difference, I'd say. And between being a thrill park and a zoo park, Busch would have to do major rebranding to operate the same way Disney and Uni do.
@Andysol 's point about resort vs. non-resort guests is a
huge reason.
That being said, I really like having the handful of indoor rides at SFGA because it's a nice change of pace, and I can duck out of weather if needed. But only because a
lot of people leave for (or don't show up because of) crappy weather at that park. If everyone stayed, everyone would flock to those 4 rides, and they'd be even more unbearable than they already are.
Though I've never been, it seems like a few indoor rides and shows at BGT would be nice for those passing rain storms y'all get in Florida every day in the summer. I think it could keep guest count higher for longer, instead of everyone ducking out?