Why are people much more familiar with Marvel than with DC?

I don't understand the question.

DC also has Green Lantern, The Flash, Supergirl, Aquaman and Shazam.

Do you mean that the DC films aren't as popular?

Because Marvel has made more film, and more people have seen those films.

Any other questions?

I reject this question. I'd say Marvel films are better quality and more Marvel films are produced in general, if that's the point you're making. But people recognize Superman and Batman plenty, as well as most of Batman's villains just as much as they do Marvel characters - and that's without having even seen the films.

Whereas, most people don't even remember that the X-Men are part of the MCU when thinking about Marvel films because all they really focus on are the Avengers.

Politely disagree. I'm sure more people heard of Aquaman than anybody following Hulk in that first list.

DC = Warner Brothers = big budget for major characters
Marvel = Disney = BIG BUDGET for every character.