It really isn’t that complicated. I mean, think about it. If you could care less about something, it does not express anything you are obviously trying to intend: Your disinterest in it. If you could care less, it means you, at the present time, care at least a little about it. And this certain amount of caring is not described in any detail whatsoever, not letting whomever you are talking to know how you feel about the subject anyway.
If you couldn’t care less, it means that your amount of caring at the present time is zero, which, well… It’s obvious. You don’t care. That’s what that means.
It strikes me as funny when a phrase is just said by so many without any thought really being given to what you’re actually saying, when you just infer that it means something.
tl;dr people be dumb sometimes.