Nothing wrong with charging for support.
I love passion projects as much as anyone, but there is a reason they are hobbies, and people need to keep a day job. Eventually it does get tiring to do support for free.
Edit:
Ok. I was talking OSS generally. I guess Redis is being bad actor if they are taking OSS work and running away with it to get the money, and not compensating the contributors. That is very wrong. I don't know history on Redis and assumed it was the contributors that founded the company.