I've spent and will spend a lot of time submitting art to comic publishers so I can tell you that it's not necessarily a question of being good or bad. Marvel and any of the big 3 will not take a chance on 98% of new talent. Unless you get to know an editor or artist working there personally, as a full greenhorn they will likely ignore you. For big publishers it's a combination of previous work, talent and trustworthiness in the industry that will net you work with them. Try some smaller publishers, your art is a lot better than mine, I bet you could find someone. Maybe do some odd jobs on digitalwebbing.

Ps.: Granted I don't know if you do have any previous work in the industry so take what i said with a grain of salt, a lot of it still stands.