Both definitely happen, but this is almost certainly a formal writing versus common vernacular thing.
As for why, I’d guess the pronunciation as a word could be mistaken for the actual word “vat” or, worse, “fat”. Most people want fat on their goods almost as much as they want V.A.T., but now there’s confusion added into the mix.
Huh, I thought VAT was also pronounced as a word
Both definitely happen, but this is almost certainly a formal writing versus common vernacular thing.
As for why, I’d guess the pronunciation as a word could be mistaken for the actual word “vat” or, worse, “fat”. Most people want fat on their goods almost as much as they want V.A.T., but now there’s confusion added into the mix.