Black Panther was not beholden to the wider MCU and didn’t even really offer much in the way of tie-ins beyond Everett Ross (who is a Black Panther character in the comics) and Bucky Barnes in a post-credit scene.
Given the level of success Black Panther is currently enjoying, it is hard to argue with any of the decisions this film made.
So people who don’t usually come out for superhero films were able to enjoy Black Panther without any need to have seen the rest of Marvel’s extensive canon, or even Civil War where T’Challa was first introduced.
People are coming out in droves for Black Panther and not because of how it sets up Infinity War or packs in a bunch of heroes, but because of the singular story and characters contained within the film.