The reason for homo marriage was never that they yearned for domesticity, but rather to force society to recognize such relationships as legitimate (since the purpose of civil recognition of marriages is to grant them legitimacy and legal protection).
Homosexuals are not generally interested in long-term relationships. They are shallow and immature people. If society grants recognition of homosexual marriage, the primary "benefit" is a rise in homosexual's self-esteem: "I can be just like everybody else". But they aren't like everybody else, so they don't really follow through on the new capability.
One thing about the rate of union that rarely gets pointed out: Middle-aged (or older) homosexuals have lived their whole lives without being able to join a legal union, and when this ability is finally granted to them, you might think that the flood-gates would open and that decades of pent-up frustration would be unleashed, with massive numbers of marriages in a very short time-frame, and homosexuals dancing in the street yelling "Finally!!"
But it doesn't work that way. Because Homosexuals are not generally interested in long-term relationships.
Regardless of the motive, they are not exercising this 'civil recognition'. That's the point.