4. The Characters Are Just More Relatable
As much as DC's superheroes are awesome and interesting, many of them are as far from realistic as imaginable. Superman is borderline omnipotent, Batman is a billionaire smart enough to take down basically anyone, and Wonder Woman is literally the creation of the Greek God Zeus.
They're interesting, dynamic characters, but also characters who are inherently 'better than' being human.
Where DC hopes to make you connect with extravagant characters, Marvel shows you figures just like yourself - and then gives them cool powers and rad adventures.
Spider-Man is maybe the best example of this, as we often see him trying to do well in school, and get a job and pay his bills, all the while balancing it with his Spider-Manning responsibilities. It makes the whole thing feel so much more real, and the universe all the more convincing - albeit, the kind of vaguely depressing realistic one where you can imagine Doc Ock doing some taxes.
In the Marvel universe, it seems all the more common for regular people to become superheroes - and that's inspiring, in its own unique way.