[devsda]

I would say practice but I think there's more to it.

For some initial numbers one might rely on memory but after a certain value we "calculate" the value and then its name automatically from small set of names for each part of a number's value.

In the case of alphabets there is no obvious sequence of alphabet in both directions. We might as well learn the alphabet in qwerty order without impacting its utility.

So, its difficult to recite the alphabet in any order other than the ones we memorized.