Not a native speaker, but I speak Mandarin. I'd say it's because to a Mandarin speaker A.P.P is easier to pronounce than 'app' (Mandarin doesn't have any sylla

Not a native speaker, but I speak Mandarin. I'd say it's because to a Mandarin speaker A.P.P is easier to pronounce than 'app' (Mandarin doesn't have any syllables that end with a p sound, but it does have syllables that start with p). There's also a history of 3 letter acronyms imported from English, such as DVD, VCD, MP3 which are all pronounced letter by letter and even though APP is not an acronym, to a native speaker it fits a similar pattern.