I run a conference myself and we manage to be 3 times cheaper with only 8 sponsors and we take care of travel and lodging for speakers. With the amount of sponsors they get, they could get away with $10 tickets like PyCon Europe which is free for all and still take care of travel and lodging for speakers. When Google gave Kubernetes for free to CNCF non profit, I don't think this is what they had in mind and may be why they went with OUC instead.
It's very expensive to run 10,000 person events, we run the events as pretty much break even across different projects, some events make money, some loss money, it all balances out. We also produce transparency reports for our events: https://www.cncf.io/blog/2020/01/09/kubecon-cloudnativecon-n...
Also keep in mind that nothing is free, running VENDOR NEUTRAL events is a hard business, ORM laid off all its events team recently during the pandemic (https://www.businessinsider.com/oreilly-media-layoffs-events...), I'm proud to say we haven't laid anyone off.
I know non-profit in the US has to fill public tax returns, i will be interested in figuring out how much execs earn at CNCF!