Since he started making appearances as a hitman and a, Deadpool's sarcasm and cynicism has become the point. Inside his own comic books, he now addresses the crowd, makes fourth-wall-bashing comment concerning the fact that he is a fictional book character and constantly has an arsenal of pop culture references to hurl at you. His speech bubbles are yellow, which implies the fact that his words, similar to the narrative boxes in books that are normal, go beyond the narrative that he is in and into our reality. Simply throw in a cavalier fighting mode, a schizophrenic identity crisis bordering on insanity, and a mutation that's, to humorous effect, his inability to expire, and you now have the ideal recipe for a uniquely hysterical character with an unparalleled level of self-awareness.
His deathlessness is a jab by the writers in the simple fact that most comic book characters are basically immortal, possibly never aging or having miraculous, resurrections that are nonsensical. It is qualities together with the character snarky, carefree character, that contrasts so well with amusing and cynical fans. It's no surprise that Deadpool's popularity has steadily grown to this point. And in a time where the oversaturation of superhero films is reminiscent of the pulp fiction which became among the western movie genre, there's never been a more apropos setting for Deadpool's super-meta existence on the screen and beyond.