Just my guess, but I would wager the following happened:
- Hagrid's was on tap to counter SW. And while it won't "beat" Star Wars, having a fresh Potter attraction was 100% the correct move as it keeps Potter top of mind and will get a great boost because of such.
- Of course, Universal also had an idea of how to counter WDW's 50th in 2021, and that was with SNW in KidZone. When they made the (I believe correct) decision to push that off to FW and have it anchor that park, it left them scrambling for something to stay top of mind. They tossed and turned some ideas for KidZone and ended up scrapping them and we are getting a JP coaster in lieu of it.
I believe the main screw up was KidZone not being addressed. Changing the 2021 counter from KZ to JP was not the right move. The JP coaster simply wasn't needed and I think it was a panic move. "We need something for 2021 and we have no concrete or good ideas for KZ. Quick, what's our next best IP we can prop up like we're doing for HP with Hagrid's? JP? Approved!" I'm excited we're getting it, but I (and I assume most others) would have much rather seen KidZone be redone.
In summary, I think they're making the right decisions with what they have in front of them right now. But I fully believe their mishandling and indecisiveness (or I suppose it's possible there was a lack of creativity) of KidZone is why we're getting what we're getting at this point.