Its only a test. Best way to get a LOT of people to test out your hardware willingly is to make it give an incentive, ie: Free Ice cream.
The data you glean helps you tune the facial recognition software even more. Instead of paying a bunch of bored broke college students $100+ each, you give out free ice cream and actually get a better representation of people.
Imagine a regular R&D Department having to spend $10k+ a week tuning the system, where instead they get the same benefit by making an ice cream run to Cosco.