Optional means unimportant content? That's a silly generalization.
I meant it has no gameplay benefit. It can't be increasingly important as a gameplay element if there's none attached.
Now, that's a contradiction. You said it yourself, companion interaction is gaining in importance. Especially if you consider that A) BioWare prizes itself in more elaborate plots than average and B) That BioWare has chosen a path of cinematic presentation - where choosing which cutscene rolls becomes a big choice. Even if you must relate everything to the primary game mechanic, combat, companion interaction its also impacting gameplay more and more.
Case in point is the Dragon Age series. In the first game the approval ratings opened attribute bonuses or even caused companions to leave you/polish your blade with their blood in case you did something heinous or they disapproved you of too much. In the second game, companion interaction was further weaved into combat as it regulates 2 mutually exclusive paths of special abilities. If memory serves, man-woman warrior tank Aveline can either become more resilient individually (because she can't really trust her her back to you) or a better tank for the protagonist, as she comes to like you and put a little more effort in your well-being.
And what else are the romances but a form in which this major game mechanic is conveyed? Then you could still argue that romances are relatively minor, and they are, but that doesn't change the fact that they grow within the context of companion interactions - and that's also where the relevance of the fandom comes in. Because it does change what's in the game.
Let's go back all the way to Baldur's Gate. You said it yourself somewhere: the developers realized the fandom was larping/modding their own romances so they filled that need in BG2. Now: fast forward to DA:O, where a couple of companions aren't love interests; the choice of gender does limit/impact on your choices of virtual concubine; and romances weren't judged a worthy addition to the game's ~20 hour long expansion. Another point of interest is how in BG2 races would also limit/impact the choices, whereas DA:O foregone that conclusion.
Now, come in DA2. The game's design and story changed dramatically. Gender no longer impacts the game, to the point where the characterization of long-estabilished characters is retconned (Anders, I think, was heterosexual); every companion, from what I read, is romanceable, even the chaste guy; and even the comparably minor DLC includes a flirt/romance of its own.
Could BioWare tie in Romances more with the game's plot? Could they add some more consequence to their choices? Sure. But to say that the choice of romance isn't that important is silly. Companion interaction impacts both the story and combat. Romances are a major marketting point. Discussions of romances and love interests produce more data in the BSN than some Universities. If anything, the C&C of romance is above the BioWarian average of "cosmetic" choices.
Isn't The Ideal RPG all about experience a story in different ways and through a multitude of paths? Besides,iIf BioWare "romances" weren't really about sex, then the actually romantic scenes would be a interesting addition to the story.
You can romance characters without having virtual sex with them.
True. That's a more personal criticism to focus of the romance plots. Its transparent in my speech there, but its in no way a universal thing so I won't bother to elaborate from here.