Pitches are a delicate process whereby filmmakers have about two minutes to convince a bunch of people on their phones to risk their careers on their idea. And when Smith sat down with the Wachowskis, they kept droning on and on about how they were "gonna invent these cameras and then people can see the whole jump while you're stopped in the middle of the jump," i.e. the freeze-frame Trinity kick. So being fair to Smith, he didn't say no to one of the most famous movies ever to go do Wild Wild West; he said no to two strangers trying to convince him to crush his junk in a wire harness for seven weeks straight.
But Smith doesn't want us to sympathize with his decision. He wants us to be grateful for it. Because even if he had been a better fit than Keanu Reeves (and that's highly debatable), there's no way he would've made up for the absence of Laurence Fishburne, the only man in existence who can look cool wearing a purple tie and Pince-nez sunglasses. "If I had done it, because I'm black, then Morpheus wouldn't have been black," claims Smith, pointing a finger at Hollywood's "one in, one out" principle when it comes to casting minorities in important roles.
Even worse (for the movie, not our racist society), Smith claims the role of Morpheus would've probably then gone to Val Kilmer. And not only is the idea of that guy giving any sort of advice to Will Smith too unbelievable even for a movie about how we're all flesh batteries for robots, Kilmer was also such a terror diva in the late '90s that he probably would've killed both the movie and the Wachowskis' career by insisting he play Morpheus unconscious like the literal Greek god of dreams or whatever. So if you believe Smith, you should thank him for accidentally giving us the best possible version of The Matrix and not, as we all do, hate him for forever robbing us of the unfathomable beauty that would've been his post-credits Matrix rap.