Aren't most people just sending files over whatsapp/signal/whatever instant messaging apps they use?

AirDrop is cool because it works offline with relatively high bandwidth using local RF. If you want to wait for you and the target to transmit all the data to/from some server 1000 miles away (using up your precious bandwidth quota along the way) that’s always been an option.

Of course, only because Apple and Google did everything in their power to prevent people sending files directly between devices. When you have a duopoly that splits the population in two parts and they can't send files between them, of course users will rely on messaging apps to share stuff.

Short story: I did a long trip across two continent with my wife. Me with an Android devices, her on iOS. We did backup our photos in our own private cloud but guess how we had to quick exchange photos while in the wild (no wifi and sometimes no network)? We couldn't. Because Google and Apple did everything so we couldn't.

Google wants to your data and fought for the cloud. Apple don't want Android users to easily partake in some data exchange with iOS users (you gotta buy your ticket to their jail). So sad you don't realize how backward that is.

Yes, because it's almost the only cross-platform way to do it. It used to be email, then pictures become almost too big to fit into attachments (and bandwidth, think about the days of 3G) and messages have less friction anyway.

Besides what others have mentioned, it's also nice for moving files between your own devices - I use AirDrop all the time for transferring files between my iPad and Mac.

Large files.

That's my first thought too, as an Android user. But Apple culture is about using what's built in, the path of least resistance, and Android/Windows are more for tinkerers who seek out their favorite solutions from a wide variety of third party options.