Actually, in other niches people make a lot less money, a lot! The only other two that make $ are Porn and RX.
There are extremely few people who make a living as affiliates in any area other than that, most just supplement income. There is a lot of room for good affiliates to make money there though – we are a lot better at getting traffic than affs in other niches.
One of the problems people have switching over from other niches to gaming is that the competition in gaming is fierce, and you do have to spend more time and money as a rule. You need to learn serious SEO to make it in this environment, and of course we can’t all be number one for online casino in the search engines.
But for an ambitious person there is still plenty of room to flourish.
I think a lot of people sign up for aff programs and make a site – and then it dawns on them that they have no traffic and that it is actual WORK to get some. So they just leave the site sitting there unattended. I know some people who have done this. I think it is quite wide spread. I think that accounts for all the totally unprofitable affiliates out there.