In times past, I imagine this would probably have been more common. In those times, if a man was gay and wanted to have legitimate heirs, or if just being married were important for other reasons like public perception, marrying a woman and having a family would make sense. Similarly, it would make sense for a gay woman to marry and have a family, especially if her husband had more money or social status. Hell, neither would even have to be gay, as marriage for social or economic reasons wasn’t unheard of and, I don’t know how common it really was, but it seems as though it would have been “understood” if a man or woman in such a marriage may have an affair on the side. The only difference for a gay man or woman would be that that affair would have been with a same-sex partner.
For that matter, I guess I could see a reason for gay people to continue to enter into a straight marriage. Maybe they don’t want to be out or maybe they just feel like the social and legal complications aren’t worth it. For religious people, I could see it making sense as well, especially if they see the behavior as sinful, they don’t necessarily have to “not be gay” but they don’t have to necessarily be married to a person they’re attracted to have and raise a family.
As for whether I’d be willing to marry a gay woman, well, it would depend. After all, there’s more to a marriage than just the sexual aspect. Why would she want to marry me? I would possibly consider it if she were a good friend and it made sense in other ways with the obvious exception of mutual sexual attraction. But right now, I can’t imagine a set of circumstances where it would make sense from my perspective, at least in my current or foreseeable circumstances.