Because it can't be implemented without low level hardware access. But also, it seems like it's a part of GMS, not of the OS itself.

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dlcarrier 8 hours ago | parent [-]

Low level hardware access for opening a file and a network port? Those are some of the first lessons in any programming tutorial. If they aren't available, what is the OS even doing?

Also, for all intents and purposes, GMS is part of the Android OS, but Google had to branch it off, to keep it closed source.

	▲	spiznnx 7 hours ago \| parent [-]
		AirDrop doesn't open a network port, it creates a WiFi Aware advertisement and a WiFi Direct connection. However I thought this also should not need OS-level changes, just android.permission.NEARBY_WIFI_DEVICES permission.