I think the reason it isn't tagged sharing is because there was no sharing or lesbian content in the first release, and no one updated the tags when the update with it dropped.
And yeah players like that definitely exist, but that's also fair enough. Some people love sharing, some hate it, some are fine with it if "their" dick is the only one in the picture. Maybe this says something about how a lot of people view women and lesbian relationships, but this isn't really the place to discuss that I think. These games are fantasies, and people come here looking to experience fantasies. For some people, that includes a harem full of women that fuck each other as well. I see no problem with it. I can't comment on the mindset of most writers as I do not know what they put into it, but I do know Lock. He does not view lesbian relationships the way you're accusing him of. You're right about players being crazy whiny about any sharing with any males though, which is a shame, I enjoy that kind of sharing too.
As for your preference in FFM threesomes, I really like it when everyone is getting it on with everyone, different strokes. If this is a problem for you, AMoB simply might not be for you. So far there's only that one lesbian scene I mentioned, but I get the sense there will be a fair bit more in the future. This isn't confirmed or anything, but its where I feel the story is leading.