Phonetic Tactics

I’m more-or-less familiar with the phonetic alphabet: “hotel, sierra, whiskey, tango, etc.”, though sadly only on those occasions where it’s not required. If put on the spot by someone on the phone, why is it that the correct words go out the window in favour of more atypical examples?

“My postcode? Yep, it’s Biscuit Acrobat thirteen, three Jam Quagga.”