Why is there no Disney logo in MCU movies?

Marvel Studios, LLC (originally known as Marvel Films from 1993 to 1996) is an American film studio that is a subsidiary of The Walt Disney Studios, a division of The Walt Disney Company.

As Wikipedia states, Marvel Studios is a film studio, similarly like The Walt Disney Studios, both of which are owned by the Walt Disney Company. These studios produce many kinds of movies and the movies which are produced by The Walt Disney Studios show the Disney's logo and movies produced by Marvel Studios show Marvel's logo.

The case is same with Star Wars:

Lucasfilm Ltd. LLC is an American film and television production company that is a subsidiary of The Walt Disney Studios, a division of The Walt Disney Company.

Here Wikipedia states exactly the same thing. Lucasfilms is a studio that produces Star Wars movies, so their logo shows up.

The Walt Disney Company owns all three studios, but they are separate entities, with each producing their own movies, signed by their logos. This company also owns studios like Pixar, 20th Century Fox, many TV stations such as ABC and ESPN.

The Walt Disney Company owns a huge number of brands. One of their brands, and one of the most famous and valuable of them, happens to share a name with the company that owns it, but that doesn't matter much. What matters more is that it is associated in the minds of consumers with a certain kind of "safe" entertainment that won't bore young kids or scandalize their parents, and Disney (the company) wants to preserve that association because it's the source of the brand's value.

While some of the movies released under the Marvel brand may fall in that category, some clearly don't, and you can't really separate them because they take place in a shared world and reference each other extensively.

It's possible that the Marvel fan base might react negatively to a rebrand. And Marvel is itself one of the most valuable brands in the world right now, being associated with several of the highest grossing movies of all time, so there is no incentive for Disney to risk rebranding as long as the status quo continues to bring in customers.

Disney generally don't put their logos on things that aren't strictly suitable for all ages. While Disney the company owns Marvel, Disney the brand is HEAVILY associated with childhood. If you see the actual Disney logo prominently displayed on something, you know it's going to be safe for kids, and also really good. It's that association that Disney uses to sell their products to parents, many of who grew up watching Disney films.

The MCU movies, on the other hand, are generally aimed at teenagers and up. The same applies to Touchstone Picture movies, which are generally aimed at adults, and ABC, which does show programs not suitable for children. There are many other examples.