The stories I've heard about the IOA previews sounds like the feeling at the time was they got burned by having too many community/passholder/TM previews and it hurt attendance when the park actually opened because so many (local) people had already been. That combined with the botched marketing of "Universal Escape".
I think the current plan is working as planned-- TMs are raving about the park already. In the next week or two their families will do the same (and probably post photos). Passholders will then do the same in the weeks after that. All this works together to sell those multi-day tickets to those who "just have to go no matter what", then single day tickets fill in the (limited) remaining space.