I am not an English teacher, but the idea here is simply one of hyperbole. I could not care less means "I have absolutely no care about that thing at all". Well, that is usually not exactly true. They usually could care less but the idea is simply one of declaring that the thing is a triviality.
Over time, and in certain populations, that declaration has evolved into "I could care less". In this use, the idea is simply, "sure, I could care less, but I don't". It is again a form of hyperbole.
Either use now means "that is an unimportant thing, a really unimportant thing, from my view".
Literally, I prefer "I could not care less". But as a practical matter, I could care less. Not sure how, but I imagine it is possible.