T-shirts are worth significantly more (relatively) in poorer parts of the world. It might be worth 0.5hr of average wage in the us but be worth 5hr of average wage in India.
Yeah I learned this lesson too. I run a coding education nonprofit and for years we have offered free shirts or stickers to people who bring someone totally new to coding (usually artists or musicians who want to work on a game) to one of our events in certain areas.
We tried it with an online event in August and it was immediately flooded with fake signups from people in poorer parts of the world.
(Honestly made me sad more than frustrated. But we're not equipped to give out that many shirts.)