Most fighting games, understandably, involve humans fighting one another. Maybe there are some monsters, but generally speaking, there's an established idea of arms and legs resulting in punches and kicks. Fight Crab does not care for such ingrained orthodoxy, to the point that its own title is itself a descriptor. In Fight Crab, that's what happens: crabs fight.
This is a companion discussion topic for the original entry at https://www.vice.com/en_us/article/wxqazb/an-answer-to-the-big-question-why-make-a-game-about-fighting-crabs