That drop would have happened no matter the movie's overall reception, though. TFA had thirty years worth of pent up hype and demand to see a true continuation of the original trilogy. TLJ had nowhere near that amount of demand, even after TFA's success.
The difference is that the MCU is literally a franchise of franchises. Guardians of the Galaxy is completely different from Black Panther, which is completely different from Captain America: Civil War, which is completely different from Spider-Man Homecoming, and so on. It's a string of different franchises, characters, and stories connected by crossovers... just like the comic books they're based on. If the DCEU actually was high-quality, it'd work just as well with its variety of characters and stories.
Meanwhile, every Star Wars movie is still a Star Wars movie. No matter how "different" these new separate trilogies are, they're still going to have a baseline of similarity to the main Star Wars formula, just as Rogue One did and Solo seems to be doing. It may have a non-related cast in a non-related environment, but it's still "A Star Wars Story." And unlike Marvel, there's absolutely no source material to pull from. Star Wars was a series that was special for not being a typical blockbuster... and now they're trying to turn it into a series that's pumped out yearly.
I could be entirely wrong... maybe the conventions of the series will be completely defied by the new series, in a positive way, that ends up satisfying fans AND the general public. But from Disney's Star Wars treatment so far... I'm not super helpful.