If we're laying it all out, even Monsters isn't guaranteed use for Universal Parks. There is footage of a main house designer given a description of Legends Collide and saying something to the effect of "We have been very gracious that we've been allowed to tell some original stories with these characters". Because as much as a lot of people love to lump Frank and Wolfman in the Original House category, they are 100% IP. There are negotiations that have to be made to make even a house like Brides happen at all.