I remember in an interview Jon Watts (Homecoming director) said he wasn't nervous about directing a huge action blockbuster because Marvel Studios is set up in a way that they can just autopilot a movie if they wanted to. So when searching for a director they look for someone who is capable of telling the character story. His secret is he built a studio filled with creative people focused on story and character first. Other studios are more superficial, if a director is successful at a comic book film therefore are perfect for all superhero films. It's the old marketing idea of all you need to say "from the director who made a movie everyone loves" and a "famous actor that has good track record for box office" then you're good. Now that may be good for marketing but doesn't guarantee a good film
Take Josh Whedon and Zack Snyder for example. Looking at Whedon's body of work it's fairly obvious he's perfect for Avengers. As for Snyder he had a hit with 300 so warner bros figure he must be right from every comic book adaptation no matter what. Like how Fox saw Chronicle's success and figured Trank would be perfect for F4, despite the fact that the type of story chronicle wasn't the type of story F4 typically is. It's much less about finding the best storyteller. You listen to people like Whedon, Russo Bros, James Gunn, Christoper Nolan, etc about making movies and you'll see a huge difference compared to how Snyder discusses it. The former can go on and on about story and character and techniques to tell tell the story and later will just talk about what visuals "look cool". That difference in hiring a director is one of the major reasons
Another reason is the concept of Cinematic Universes is pretty much a gimmick. Whether it's a good gimmick or a bad gimmick depends on how it's done. Marvel Studios is always more concerned with making sure the film they're working on is good and not getting distracted by something 5 films down the line. When Whedon came a board he said he'd only do it if he got to write the story and Marvel said go for it, the only constraint is that it has to be about Loki using the cube to unleash an army in NYC and some else has to be behind it. Everything else including who was behind was up to him. So the whole Thanos and Infinity War was started by Whedon instead of the studio. When making Guardians vol 2 James Gunn said infinity war had no influence on it. He wasn't writing a movie to set up the Guardians for a future film, instead the future film was going to be written around what happens in vol 2.
Compare that to the DCEU or the Universal Monsters. Both BvS and Mummy were far too concerned with universe building and setting up future films than just telling a singular good story and those movies suffered for it. Just studio's desire to capitalize on the cinematic universe craze with the concern of telling a story well.
That's the key difference between the Studio Fiege developed and other film studios.