The registrar can simply raise the registration price of Wikipedia.org to a million dollars a year, and keep the random ones the same price, to extract any value from .org websites that rely on their domain name. The 10% a year is not a legal commitment, just an easily breakable informal promise.
If their registrar did that, Wikipedia would change registrars to one that didn't - and they'd be able to keep their .org. There's competition among registrars, unlike registries.
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".
For example, Namecheap came out strongly against removing .org price caps: https://www.namecheap.com/blog/ensuring-icann-keep-domain-pr...