One of the two is a foreign national and has worked here for years and has been waiting his turn in the legal immigration line.
I'd guess Pelosi and the rest apparently want to have those cases treated "equally" with those of legal heterosexual marriages.
They also see it as a way to bring in more foreigners.
As you know, if a an American marries a foreigner that foreigner is allowed to live in the United States. The dems want that to be for men and men marriages too and lesbians.