I think the thing that makes an OSS implementation more difficult than iOS/macOS is the friction involved.

Say you've got an android phone, windows PC, and a linux box, and you want to be able to quickly drop files from each one. unless we get some kind of cooperation across all three platforms at the OS level, you'd at minimum need to install some kind of client into each system - when the nicest feature of airdrop is that it's baked into all of Apple's OSs, in my opinion. even if it worked exactly the same way, but had to be installed, I think it would see less use - and there's no real way for a single OSS project to do that across multiple OS platforms, to my knowledge