The MCU has used crossovers as their major cinematic features up until Phase 3, and they’re right to break the crossover obsession. Avengers: Endgame was a huge cinematic moment, with every crossover possible from the Marvel universe that had been building up in the Avengers storyline, separate from each character’s story. Alongside the main storyline, characters had their own films and storylines, starting with Iron Man.
Phase 4 has seen the MCU expand as the universe - and the Multiverse - has started to develop. Although there is still some crossover, like Wanda appearing as a hero and villain in Doctor Strange in the Multiverse of Madness, the structure of the MCU is now somewhat different. Whereas Phases 1 to 3 had the Avengers movies be the main storyline of the universe - with the various individual film lines serving as tie-in stories - the Phase 4 universe is different, allowing for installments that are less directly connected to the "big story" of the current MCU.
Marvel is right to break the MCU’s crossover obsession in this way, because the MCU now reflects Marvel comics itself more accurately. Not every comic book reader reads every title, and similarly, not every member of the MCU's audience should feel obliged to watch every movie and show. Some who enjoy the spy stories that MCU's Black Widow provides may be less interested in the supernatural aspects of something like Doctor Strange. Moving away from the interconnected nature of the franchise allows the MCU to gain more breadth and have a variation of stories that differ from each other in all aspects. Because of the number of crossovers, cameos, and guest appearance found in both the MCU and DCEU, as an event they have become more expected by audiences, making them less special. With this in mind, even a temporary change to this formula would seemingly serve in the MCU's best interests.
Also, doing this means some audiences are not excluded from the MCU, or otherwise confused at how to approach it. With the number of releases both in cinema and on Disney+, it can be hard for audiences to watch everything, particularly with the introduction of series and One-Shots, that Phase 4 has finally made matter. Not making changes for Phase 4 would mean a portion of the MCU audience could have found the main films themselves less satisfying, as it would have required people to watch all the Disney+ MCU shows - which naturally some people simply don't want to do.
However, having Avengers-level crossover films are integral to the MCU, as well as a big selling point. It would likely be impossible to entirely get rid of them as Phase 4 has forever, as one of the main draws of the universe is getting to see beloved faces fight alongside one another. There is an excitement for audiences to see their favorite characters interact with each other, and see how the universe connects, meaning the crossover elements of the major MCU are sure to pick up on some level once more in the franchise's future.
These forms of connections are still possible to carry off while ensuring Phase 4's careful universe adjustments still hold true, however. For example, easter eggs are a great way to feed audiences' desires to see how the MCU connects without alienating audiences who don't get the reference, and thus leaning more towards this subtler approach for a while could benefit the overall product. By approaching the interconnected nature of the MCU more cautiously in the immediate future, the longevity of the franchise may well become more solid than ever before.
