Fair enough, but I think if you look at it from the developer's point of view, they are trying to get a minimally viable product in front of their target market

Fair enough, but I think if you look at it from the developer's point of view, they are trying to get a minimally viable product in front of their target market - which happens to be immense. Yeah, sure, some people might be inconvenienced by not being able to use this without Facebook, but for now, they have an easy* way to connect with the vast majority of their target market. *easy used relatively here