No, you are wondering why they are not. But due to your G-d given limitations, you are incapable of understanding why they are not.
I'm not wondering why they're not.. you are.
You're ******* deranged.

What have I said that would lead a nut like you to
think I'm wondering why none of those other forms of marriage aren't allowed? Especially considering I tried explaining to you, to no avail, why they are not allowed.
Meanwhile, you're here questioning why they're not allowed. You really
think you can transfer project your short comining onto others?
You are the one questioning whether they can be allowed, I am the one explaining how the Constitution works. You seem confused.
If you have, by law, distinguished a "group" ...in this case, homosexuals... as having a right to define their relationships as "marriage" and be legitimized by government as such, the same right must be afforded to similar "groups" ...in this case, other 'harmless' sexual proclivities. The only issue currently standing in the way is the legality of these other sexual proclivities, but as was pointed out, homosexuality is only 12 years removed from being an illegal act.
Now, we can look to all the case law surrounding how homosexuality 'came out of the closet' and became legalized... it was not a compelling interest of the state to prohibit it. The very same argument can be made for other sexual proclivities... most of which are currently illegal because of religious moral views.