An anecdote: I easily remember short-ish (pins, phone numbers) number combinations, learn completely new alphabets of new languages easily enough, just like their words, but I struggle to learn the NATO alphabet: the words have no meaning and I don't perceive them as atomic enough like a letter or number is, so it mostly looks like a large amount of random noise to me, like having to learn pi to 100 digits.
I forced myself to learn the NATO alphabet recently by using some online flashcards. Nothing complex, just shows the letter and I have to recall the word, then click to see if I got it right. Didn't take very long to get it down, and I go through them every few days to verify recall.
