The more logical reason would be that they don’t want to have to deal with the legislation in regard to that kind of content and there might be pressure from third parties. In particular payment providers that have a historic low interest in being available for adult oriented media.
There is also that, now, old conspiracy theory about the crew from Campo Santo talking the helms of this part of the approving process. And being a little trigger happy with it.
But no matter the reason. It just suck for developers and players alike. Developers have this tremendous issue with developing games that might not even be approved by Steam or even being pulled out of the store with very reason given. While players are basically left hanging with titles getting canceled.
And what make it even worse is that in a global scale. There isn’t really a option on par with Steam. Not only in terms of the tools that they provide. But for the consumer most of the other options don’t have basic features like regional princing or regional payment methods. Making them inacessible for a big chunk of the market.
