What if every phone could copy-paste an Airdrop implementation?

That's apple's decision, one of many to force their users to only get their devices, similarly not being able to host your own game servers benefits the publishers/ devs. (Edit for clarity: by this I mean that this state of things isn't caused by unavailability of open source solutions but rather by corporate greed.)

"Owning" algorithms and hiding implementations is such an absurd concept.

Not any different from protecting one's art creations. You spend a bunch of time learning how to code and are doing it for a living so you don't want others/ competition to take it and sell as their own. Not sure what's hard to understand.