She's so smart and pretty...

Because she is secretly a Hunger. And you don't want to stick your bread in that oven.

Because Altmer fans would only marry her. Instead they got an old Altmer called Taarie.
And Bethesda probably hate Elves.

Because High Elves are all evil Nazis, and we should hate them and WANT to exterminate them cuz Nords are Vikings and cool.

TLDR: Because raisins.

Ni, I'd say because of wine

You could have, you would have done a quest for her, then she would be eligible for marriage.

Because she is your teacher. Even if you have decided never to go there she will perennially be your potential teacher. Now, you can become the archmage within a week, which is silly, if you could also marry the most notable element of the college that fast, I'd be really worried.

Edit: now that I think about it, marriage should have been a huge mini game, a romance where you are "fighting" for the hand of your chosen day by day. At least it's better than how it works now:

Guy: AY GURL AY

Girl: w00t!

And they lived happily ever after.