Reasons why Wizarding isn't open based on what we know/intuition --
--It costs a substantial amount of money to run Wizarding World fully-staffed (which it would have to be). While the land generates money via merchandise, Butter Beer, and other food/bev, Uni might have deduced (from their test last year?) that profit />/ operational cost.
--If the Orlando situation is any indication, Uni has to pay JKR/WB a portion of the gate price if Wizarding World is open. That's a slice of every HHN admission media that leaves Uni. Gotta factor that into whether or not profit exceeds operational cost.
--Finally, could motivate stragglers to not purchase a daytime ticket and instead visit Wizarding World during Horror Nights - i.e. much of the rationale last year.
That said, they did run the test the final night of the event. (It was a major relief on operations, that's for sure.) They were clearly considering having it open at some point.