There are people out there who will assassinate someone for a thousand bucks. That's doesn't mean everyone will do that, in fact most people would physically throw up, or faint, as they went to pull the trigger. But, fact is, a small percentage would do it for a grand.
There are BILLIONS of str8 guys. I never believe those who say 0% will bend over and take a cock in the ass or deep-throat a fat cock. Most would not, sure. But there will always be a few with the ability. And some people are just horndogs - the mere act of sitting down gives them a hard-on - especially at age 18-21. And a grand is enough for some.
Some gay men believe that having gay sex = being gay. I believe that is because they were bullied at school by straight guys and so they label all straight guys as x y or z. No exceptions. Believing such an extreme view is abnormal. I have seen gay guys on the web being quite passionate and bitchy when anyone suggests one of their favourite models is probably gay4pay.
Also, the view that str8 guys will not do gay porn is a very upper/middle class view. Quite snobbish. Try living in a country will very little social protection, and where you sweat on a building site for a month for 600 or 700 dollars. Where your little car badly needs new tyres in case a cop pulls you over and you need to keep that car on the road. A guy can work for a studio like B€lam1, and do 15 scenes at a grand a pop in the space of a few months. That's enough money to buy a flat outright in some countries. Certainly enough to buy new tyres for you car.
Also, it is not always having to suck off some dirty old man fat and wrinkled. Mostly actually, you go into a studio and meet up with other 18-21 yo or so guys and basically see the lighter side and have a laugh. It is for these guys, just a job. And in any job, time passes quicker if you lighten up.
So to all those who say 0% would do it, out of 4 billion or whatever, message is... lighten up, but believe whatever you want. If you want/need to believe they are all gay go for it. Statistically it is super unlikely no str8 guy have ever done porn - and I believe lots have. But as to any one actor? Who ever knows. It will be someone you have never even met so how would you know one way or the other?