It is tempting to blame diversity which can be part of it but I'm going to blame a cabal of like-minded people who decide who writes for the big two. That highlights another problem. The west, or rather America, is just the same few characters written over and over again telling the same stories again. Capeshit as someone already said. Japan manages to have anthology magazines in which chapters of various stories are published together. France manages to have range of stories in their Bandes Dessinee besides some regulars like Asterix.