That's because a harem must have a center. The fact that Sam is easier to deal with than Bobby, and that in a way Sam also enters Lincoln's harem, if the target audience here weren't primarily heterosexual (or female) and Bobby also entered Lincoln's harem, this would be resolved in the same way, reconciling polyamory and the centric harem.
But it's not a plausible solution because it's inherently unappealing to a heterosexual male audience (and by nature, not because of any kind of "homophobia," it's simply how the attraction and rejection system works in heterosexual men biologically, and because we are different. Homosexuality or feminine nature isn't just a redirection of libido to another source, but manifests itself differently as well).
