You've heard the term "there's no accounting for taste" I'm sure. I think most people find that caffeine free Coke tastes quite different, I know that I do. The process of removing caffeine must change something.

It tastes a little sweeter
Seems less carbonated

Sweeter and less carbonated combine to make it undrinkable.

Caffeine free Coke is like warm Dr Pepper. How's that for illustration?

Warm Dr Pepper is barfmaking.
Ice cold Dr Pepper is nectar of the gods.