I was more questioning why they didn't add flirt options with Solas like they did Cullen rather than why he wasn't available as a romance to males/other races. But I do really like the idea that he wanted to give a meaningful elven gift...he was real catty with an Inquisitor who romanced Sera, saying she'd want something "human and fleeting" so he definitely isn't the simple gift type. Too bad we didn't get to return a gift. Didn't the other romance options get a return gift? Maybe the relationship with him was the gift. Or maybe...we'll get to give him a gift...in the future.
I suppose the lack of flirt options is probably due to lack of time to add them.
As for a return gift... I am hoping we get to do something with Solas in a DLC, hopefully that doesn't end in tragedy. I still have my suspicion we're going to be asked to have elf babies with him in the future. Yes, I know not all women are fertile and not all women are female (gender vs. sex), but as long as it's a choice and not something forced upon the player, well... I'd be okay with it.
That said, I'd have liked to have been able to give Solas some kind of gift. I guess it'd be hard to give someone like him a gift, though. Material possessions don't seem as important to him--his reaction to the Inquisitor asking about gifts for Sera tells us that. It would be more about the meaning behind the gift, and something "human and fleeting" wouldn't be enough.
Speaking of "human and fleeting..." If he's against that kind of gift, no wonder he wanted to do something like taking away the vallaslin, which would be a permanent change. He's making a statement that his love will last as long as his gift does. That's kind of... He's trying to tell her he'll love her as long as she lives, right before he has to leave her, forever. That is profoundly, horribly sad.
... Solas, why do you have to be so adorable, you messed up elven god, you?????