I'm sure that Docker Hub is expensive to run, and the core Docker app isn't free to maintain either.
This TOS change was a fiasco, and absolutely didn't succeed in doing anything other than losing a lot of community goodwill. But I do understand why they're trying to squeeze some money out of Docker Hub. I'd be surprised if it's even break-even for them right now, and VC funds aren't exactly known for their acts of charity.