Sometimes you just want a good story, capably told with no time to waste.
www.vulture.com
There are MCU and DCEU films shorter than 2 hours, and Birds Of Prey is better than many of the ~2:30 hour films. Then there are shorter comic book films that are great like Dredd, The Crow, Batman Beyond: Return Of The Joker (74min!), Batman: Mask Of Phantasm (76min!) and more. Then there are non-MCU flicks like Spiderverse, X-Men and Deadpool. 90 minutes can be perfect for comedy, action, horror, thrillers, or even dramas (Ingmar Bergman), the script just have to be leaner and more focused, on the core theme and there will be less plot threads. Considering the unanimous criticism for the film was about the tone and mismatch with the themes, I think it would have helped to focus more on less stuff. Not every MCU film has to have several plotlines, cameos, crossovers, otherwise you end up with sequel bait and half-baked endings or things not feeling complete. I would assume filmmakers would like to make shorter, leaner, and even standalone films. Multiverse Of Madness could easily have been just about Wanda and Strange, and just be straight horror.