Honestly she was one of the few characters in the game that I felt had enough depth and interaction with the player that marriage could make sense.

Pretty much everyone else is like “oh you fetched that alchemy ingredient for me? Sure I guess I’ll marry you, I’ve got nothing else going on that day”.

Don’t get me wrong- i still love Skyrim and I’m perfectly happy with marriage being basically just another quest that gives you some buffs. It’s just funny to me that Serana is one of the few characters where we can learn a TON about her, meet her parents, go exploring together, share interests, wash blood off our hands together, eat food together, go on dates. She’s accomplished enough that she is not at all intimidated by the Dragonborn, rather relates to them for being granted these supernatural powers and responsibilities they didn’t ask for. My first time playing Dawnguard ii really thought the devs were hinting that she would be the canonical spouse of the Dragonborn moving forward because it makes so much sense. So I was quite surprised she wasn’t eligible.