Because it sounds strange to put two vowels next to each other like ‘ma application’, so the masculine possessive is used instead, to create the liaison (letter ‘n’), which makes the sentence flow easier when spoken. Remember this applies too ...

Before verbs, this question would be a duplicate as mentioned in the comments. (usually “avant de” + infinitif présent; après + infinitif passé) Before nouns, “avant” and “après” are directly followed by a “noun group”. This noun group will be ...