Chebucto Regional Softball Club

"Should they?" No. Games are a form of art, and they have no obligation to be anything more than what they are. That said, if their goal is to reach as many players as possible, they will miss out on a (likely) growing demographic by excluding PvE, especially if the framework is already there. Many people have no interest in duking it out with sweaty tryhards, and even if a game is lucky not to have those types, there's still people who make it their mission to grief others whenever possible. So I don't think they "should," but it's shortsighted not to.

Xbox: Embrace, Extend, Extinguish! Also Xbox: ...wait, were we supposed to do that to other projects?