Ant-Man is a more marketable character than Black Panther, though... even though he isn't a high profile superhero people pretty much know what he can do from the name, and the trailers showed you that he shrinks, and it looked fun. The appeal of the concept is pretty obvious. It could draw in people who don't religiously watch every Marvel film (they do exist, I know some). So they didn't really need to build him up over two earlier movies. Whereas Black Panther.... his superpower is.... he's black? I've seen Civil War and Ultron and I can't remember! Of course a black superhero has other kinds of appeal but I think the character lacks a hook, power-wise.