It's not common, but a thank you token has happened before. UA used to do similar many years ago, and DL and UA used to supply agents with drink vouchers for modest accommodations.

Remember the volunteering business is a market, and it makes sense to keep potential volunteers happy and interested. Lowball the compensation and some passengers tune it out and it will cost you more. We're in a strong recovery scenario where there are fewer backup options and people are less money sensitive because they've banked up cash for the past year plus.

I used to VDB quite a bit when it was more reliable, but I've sort of tuned it out over the past few years because everything was always over and they'd almost never need, plus with online/kiosk solicitation, it cost them nothing to request vols, so they seemed to ask for even the most unlikely scenarios (e.g., over by 1 out of a hub). UA is the biggest offender on this, soliciting if the flight at any point in the last 24 hours *was* over, even by 1 (even if it's under by 10 right now). So I lost interest in leaving the lounge early and waiting to board just to find out they won't need me again because no reasonable person expected it to be over anyway.

A consolation prize for trying absolutely makes sense to keep the "pool" of interested VDBers as large as possible to help the airline.