Their margins on new domain sales are thin, but the cost of changing domain names for a big owner of a prestigious .org domain could be huge. So jack up the renewal price to gouge existing domain owners, then drop the prices again to entice in new registrants.
Or follow the model of banks profiting off of debit cards by charging exorbitant fees for common mistakes. They didn't need that a high percentage of their customers to pay overdraft fees before they were making billions. Forget to renew your domain on time? No problem, we've held on to it for you, just please pay this $150 "redemption fee".
If a registrar did that, the .org domain owner would change to a better registrar, and they'd be able to keep their .org domain. There's competition among registrars, unlike registries.
