They exist to deliver a particular experience to the user. Calling them "boyfriend", "girlfriend", "romantic partner" etc is just propaganda because the user is not engaging with an independent entity with its own goals and desires who chooses to be with them. It's just an edited, sanitized experience meant to evoke "romance", like how some video games evoke war, racing, or running a gigantic, world-spanning factory.
Nothing wrong with enjoying an experience if you're not hurting yourself or anyone, but I wouldn't be surprised if addiction is a big issue here. And addiction does hurt ppl.