Well partially, yes, it's humor was not aimed at all quadrants of audiences and trying to appeal to everyone, which Marvel movies do, which is why their humor has a certain baseline of safe unchallenging pleasantness to it.
But beyond that, Deadpool is a fourth-wall breaking film that, ironically, really develops Wade's relationship with Vanessa, and their romance is intentionally not wholesome or meet cute. It's just not that there's nudity or sex--although the fact that it includes a scene of Reynolds getting pegged is pretty amusingly out there, especially in a superhero movie--it has a bit of an unsavory quality that is refreshing given how blandly innocuous superhero movies are. And the real climax of the film is Vanessa seeing his face, not Wade fighting Francis. Also of note is the fact that Wade is the only funny one and self-aware that he's in a movie character. Everyone else is playing it fairly straight.
I just compare that to the nonstop banter in the Marvel movies, even ones I love. I do love the first Avengers, but there are no stakes. They are fighting over a MacGuffin (the Cosmic Cube) and supposedly the world is in danger, New York will get nuked, but no one is taking it that seriously even in the third act. "We have a Hulk;" "Hang on Legolas;" "I'm bringing the party to you," "That doesn't look like a party;" "This is just like Budapest all over again," "You and I remember Budapest very differently;" "Puny God."
For the record I loved that movie, still enjoy it, and am fine with all that banter. But when every one of their movies do that during the third acts or nearly ever scene, so that audiences never get bored or find the proceedings too intense, and it is always the same kind of lighthearted inoffensive most basic comedy, it gets really tiring after awhile.