Marvel soundtracks don't stand out with memorable risk-taking music for several reasons, but Every Frame A Painting names the key culprit: temp music, also called scratch tracks or needle drop.
Most people can't look at a blueprint and envision the building. That's why computer renders for proposed buildings are ubiquitous now. The same is true with filmmaking. In order to sell a cut in the studio bureaucracy, or even shape a scene, it's much easier if the cut has temp music. It's also easier to shape a cut if you use existing music, especially music that has worked well for other films. In the industry this is called "borrowed interest." That's why you hear a million trailers with the same music, whether it was Yello's 80s "Oh Yeah" song popularized in Ferris Buehler's Day Off, or the 28 Days Later theme, or the Requiem for a Dream theme or the Inception theme.
Marvel films almost invariably go with the risk-free option, sort of a musical McDonald's menu where you know exactly what you will get emotionally based on the music matched to the scene.
Tons of great examples in this well-researched video.
• The Marvel Symphonic Universe (YouTube / Every Frame A painting)