I definitely agree there was something "there" between them in the beginning. The story for JLO was massively altered early on so I think it's quite likely there were plans for a Cy/Star romance that got cut, especially since it basically got turned into a Jessica Cruz book with little room for anything else. Wouldn't have been opposed had it happened, it's just the TPTB are too incompetent and nostalgia-driven to make it work long term.
Starfire is so heavily pushed as Dick's main love interest on TV and now live-action that even if they barely see each other in the comics, there's gonna be hesitation to have her move on in any significant capacity. It's a huge disservice to her character and one that prevents a relationship that could enhance another Titan as well, but it's one to consider if we're looking at it from the perspective of building a Cyborg "franchise".
Which I agree is unfortunate. As others have said, it makes sense and has potential. Though you never know, I think the chances are high that Vic ends up back on a Titans roster in the near future and maybe someone'll have enough balls to put them together. If it's well executed, who knows, maybe it can last at least for a bit. Being fearful of nostalgia hasn't seemed to help DC anyway so why not?