The only thing that doesn’t explain USS’s focus on Horror Nights... but I do see your point. Singapore will always feel a bit removed from the other Universal resorts without Potter. But cartoon characters would be a better marketing draw for families, I suppose.
The Singapore park seems like a relic from a previous management team. I really doubt Universal would want to buy the park outright, unless it can get the hotels in on the deal, which is unlikely considering the owner.