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.