
I do think is for what you said, it all depends on her interesting, maybe at first they were blobs, but she never bothered to bond with them or to get to know them, as she only had ML.
I know people say is because they had no roles in the romance setting, but they did have roles, maybe not protagonist, but they had important enough roles such love rivals, bullies, antagonist, Ml's friends, and family, which are characters that keep pushing the story forward.
Roles important enough for Fl to know their names, but yet they were blobs, that's why at least for me, it makes sense if she couldn't see them because she did not see them as humans.
I'm loving this story but I really hope the explain why she can't see other people. Is it only after she finds them useful? So exciting