The point of Airdrop is that the devices don't need to be connected to a mutual wi-fi network or to know one-another's IP addresses. They just need physical proximity. It's not for sharing data with established contacts; it's for cases where you need to pass data to people you're meeting for the first (and probably last) time, without any setup.
You just have to configure hotspot on your phone and there you have it. Still easier than asking someone else to install an app, especially if that person doesn't have access to mobile data.
And if it is short textual data it is more easily shared with a qrcode.
