While watching deleted scenes from comic book movies can be fun for the most devoted of fans, sequences that don't make it into tent-pole Marvel movies end up on the cutting room floor for a reason.
Scenes cut from kids' movies are usually axed because they are a little off-putting, like the deleted scene from Home Alone where Kevin gets pantsed by his uncle. Some deleted scenes from sci-fi movies make the special features list because they were too hokey, like when a xenomorph does the crab-walk in Alien. Deleted scenes from comic book movies may have been left out due to similar reasons, but sometimes they need to be cut for continuity's sake. The complexities of shared superhero universes don't leave much wiggle room for extra scenes or storylines.
Marvel movies lead the pack when it comes to deleted scenes, but comic book films from all publishers and studios have their fair share of embarrassing clips they were wise enough to leave out of the final product.
The morbidly obese vampire from Blade, who the vampire hunter roasts with UV light, evidently got so fat by eating children. A deleted scene shows the corpses of said children littered around his hovel when Blade (Wesley Snipes) enters. David S. Goyer, the screenwriter, originally had the detail in the script because "I figured that Pearl was obviously too fat to get out of his bed, and that people would have to bring him bodies."
The Wolverine was a decent movie with just enough violence without going overboard. That almost wasn't the case, though, because a deleted scene showed a random henchman get chopped up in a snowblower and sprayed out in a mist of blood during the fight scene in the snowy village. This is around the 1:14 mark in the video, if you're curious.
Norman Osborn (Chris Cooper) was just briefly in The Amazing Spider-Man series before dying off-screen. Sony was apparently planning on bringing him back, which is why his severed, frozen head was in a deleted scene, further setting up the Sinister Six movie that has been stuck in development hell. Originally, the scene was supposed to act as a post-credits teaser.
While Peter (Andrew Garfield) mourned for his lost love, his dad, Richard (Campbell Scott), was going to show up and console him in The Amazing Spider-Man 2. Not only that, but he actually was going to give Peter the "With great power..." speech, which even the most causal fans know by heart.
There were already enough subplots in the movie. Richard Parker didn't really need to be another one. His dad was supposed to give him the strength to put on the Spidey suit again in the scene. Sony was trying to create an entire ASM universe, so it's no wonder they initially tried to stuff so much into the movie.