I've wondered if Cullen wasn't originally intended the straight female/gay male bi option before the clamoring began for Qunari romance, and they decided to un-race gate Iron Bull. Cullen and Josie would have been something like book-ends, bisexual advisors available to players who wanted a "sweet" romance. Unfortunately, making IB the bi romance left heterosexual female characters with a choice between someone who would leave them lying naked and alone in a barn and someone likely physically to injure them. Coming on the heels of ME3 I think Bioware rightly judged that releasing the game in that configuration was not in their interest and partially restored Cullen so that straight female characters would, like every else, have access to a "nice" romance. Other characters can romance either Josie or Dorian, who may not be to particular players' tastes, but who don't come with what some players were likely to consider actively offensive baggage.
The Solas romance, I'm guessing, was added more for lore/story reasons than to provide players of female elves with another romance choice, and I'd recommend that any player actively interested in lore experience it, regardless of their sexuality.