> It's simply not possible that two different things can both be true? That ISPs already have to do it so should disclose what they're charging, but that also the number of taxes and fees are ridiculous? Why is that so hard to separate in people's minds?

As several other people told you, because they can get it right on the bill but not on the contract and advertising. If they can do the first, they can do the other two but they don't want to.