The reason is that "Gay Marriage" isn't marriage at all. They're trying to completely destroy the meaning of the word with this. There's no other reason for it.
It's a core part of the Left's attack on the family. A family is defined by a marriage, so if you can render the term meaningless, then family is meaningless too.
First the word "marriage" will be diluted down to "more than one person, living together, or not, and in a relationship, more or less." Then the word "family" will become something like "some people who may or may not live together and may or may not be related, but want to be treated like a family".
As Rush is fond of saying, "Words mean things!" and "marriage" means a man and a woman committed and bound to one another 'till death. (at least)
so who died in rush's marriages lol.
When marriage means anything and everything, it will mean nothing. That is why they won’t stop pushing.
It appears we Californians got this one right for once.