Radio Netherlands Worldwide

I would say there are a few reasons why gay men are not marrying as much as straight couples.

Some of my friends are opposed as they see it as a conservative patriarchal construct that is oppressive to women. In getting married it perpetuates and reinforces this construct. They see marriage as a regressive action.
Others see it as state sanctioned intervention on your personal life.
Others realise we are different, two men are never going to conceive so the desire that straights have to wed then populate is not strong. In fact they never grew up all gooey dreaming of marriage and children. They spent most of their time thinking of that hunk of a man.
Others DO NOT want children. They see the raising of children as a taking too much time and energy.

Finally the aid gay men give to their siblings, parents and extended family is a serious thing. Some scientists believe the individual who give assistance to the tribe has allowed some communities to thrive more than others. ie. if you have giving (non-married) individuals in the family they can make the difference of your family succeeding or not.

In my case I assist emotionally, financially etc to my siblings and this children and my parents. If I was to marry, my tribe would suffer as my resources would be focussed on my partner and I.