Right, this is why I've referenced Frozen Ever After a couple of times. It's not a very good attraction, but because people love the Frozen IP it gets relatively long waits -- that's partially because of its low capacity, but as I said above, it's not as though Maelstrom got similarly long waits so someone can't claim it's solely due to the low hourly capacity.
IP is a great way to prop up a mediocre attraction. It won't save an attraction people just don't like (Little Mermaid is often close to a walk-on even at busy time, and although it's an omnimover with higher capacity, Disney certainly expected longer waits or they wouldn't have built the queue they built), but from a Disney business standpoint, a mediocre IP attraction is absolutely a better investment than a mediocre non-IP attraction.
It's certainly one of the reasons the IP mandate exists. Overall quality is less of a concern when the IP alone can draw people to an attraction. And no, I'm not suggesting they're going to intentionally build mediocre attractions -- just that it's a safety net.
If I was running Disney parks in the current corporate environment solely from a business perspective, I'd probably have the IP mandate too. There's just no real downside to it in the short term, especially when the goal is quarterly growth. Any potential long-term issues (which are less about the IP mandate and more about other quality issues throughout the parks anyways) would likely not be my problem.