Well, there's a major difference other than "market". The very form of the property is different.
For superheroes, the base and central unit is the hero, the character - Captain America, Iron Man, Thor, etc. When we say "D&D movie" the first thing we think of isn't an iconic character, but a more generalized experience of a game in which the audience is a major creator of the experience.
And that's a real problem for a movie. We automatically lose the central aspect of D&D - the audience-as-creator. And we don't have a stock of well-established characters to focus on instead. So, the D&D property doesn't actually give what you need for a successful movie - characters. It gives a bit of marketing cache if applied properly, but doesn't otherwise bring the important things to the table.
IMHO.
I agree completely.
Furthermore, I think that marketing the movie as "a Dungeons and Dragons movie" is attractive to fans, but not to mass audiences, do you agree?