It's also probably worth looking at the development timeline as well. Disney bought Star Wars in 2012 under the pretense that Star Wars is one of the most lucrative brands in the world. Star Wars was an evergreen property and proved it's power for 30+ years, while there was properly concern for Marvel's timelessness, whether superheroes were a fad, etc. Also, while the Avengers hit big, Disney still didn't have access to some of the biggest properties like Spider-Man or the X-Men, both in film and in theme parks. So, there was probably the decision to go with the safer choice first in Galaxy's Edge, a proven brand they had full control over, and wait and see if Marvel had the staying power to justify navigating the rights.
In 2015, it seemed like they were right; Force Awakens was the highest grossing domestic movie of all time (unadjusted) and top five worldwide. That same year, Ultron was successful but failed to outgross the first Avengers movie. At the time, it looked like Marvel found its ceiling, while for Star Wars the sky was the limit. Fast forward to today, the situation is obviously completely reversed. Endgame is on track to be the biggest movie ever, while Star Wars, still popular, shows its not infallible with Solo flopping and an inability to penetrate certain international markets like Asia.
I don't really blame Disney for prioritizing Star Wars in the parks, as they were just working with the safer option at the time. Like, who really thought Star Wars of all things would be supplanted in popularity in less than three years?
Bringing it back to MSHI, Universal has like zero incentive to add anything to the land. The merch in the gift shops will sell anyway thanks to the popularity of the MCU, so less upkeep and the rights payment every year, it's basically free money. Just like Disney, they most likely prefer to focus on in-house IPs or juggernaut brands NOT owned by a competing theme park down the street.