Why I can not play rating games, apart from standard, in correspondence chess?

I want to play rating games in chess960 or maybe in other chess variations in the correspondence mode. Apparently that is not possible. But I have the impression that is possible for other users. If I am not mistaken I saw some in the search list. What are the conditions?

Don't get what you mean. Just click the create a game button on the main screen, under section of "Correspondence".

That's only half of the truth, the button change to "unrated" if I select "chess960" or other chess variants and I can't switch it back to rated. Try it!

Some variants can be winning for White by force, such as atomic. Atomic starts with +3 eval for white and with extended time for sides to think, White should just win every time. There are also some 960 positions that can be unbalanced with extended time. This is probably why there are no rated variant correspondence games.

Well, then a rating system for chess960 wouldn't make sense at all. I don't think a rating system for chess960, even in correspondence games, is a stupid thing. I see here no significant difference related to different time controls.

And if you really think that rating system is nonsense you can always choose the "unrated" option.