Rio Tinto and gay marriage

I was watching TV on the weekend and I saw a man get down on one knee and propose to another man. The crowd looking on was exhilarated and in rapture for the happiness for the couple.

At the end, I learn the ad was brought to me by Rio Tinto.

Why are these guys trying to promote this? What commercial advantage is there? What lack of opportunity is there if they don't?

Please explain.....