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.
I just airdropped 130 photos from my phone to my coach and I was sure it would take forever. The preparing stage on my phone took maybe 10 seconds, and the actual transfer took what looked like 2 seconds. I couldn't believe it.
I know there are better ways to transfer stuff. I am just saying that a majority of people don't tend to use them regardless of how easy/compatibles alternatives are.
They naturally choose to transfer stuff from the same app that they are using to communicate with others.