I meant more broadly: no one's reimplemented AirDrop, and MicroG won't have this new one for quite a while.

Did people used to widely reverse engineer protocols that weren't related to communications and chat?

Doing it to a chat-app has an obvious benefit: you can use your own application with your custom UX, and connect it with multiple networks at once, or multiple accounts at the same time on the same network.

Doing it with something like Airdrop is kind of a nebulous proposal. If you want to share files with someone next to you, and for some reason you hate Airdrop, then there's lots of other alternatives. Reverse engineering Airdrop gets you nothing special.