I work a normal job.... Open source is a couple of hours a week at most. It's a hobby for me some months I do nothing other I crush bugs like it was my job.
The problem is that big OSS database projects have teams of paid developers working on them and they want to make their money back. You can do this by offering paid support or a hosted offering. Having someone like Amazon take your product and build their own hosted version really cuts into that revenue.
Now, Redis was AFAIK pretty much just written by antirez and maybe it could have stayed that way, but even exceptional individuals clearly want to move on eventually and you'll likely need a team of maintainers. Distributed data products are complex and need people who contribute more than nights and weekends.
The best open source software is developed by unpaid people. Even the ones with companies around them, the best work is done in the first phase when everyone is still unpaid.
The "cuts into their revenues" part usually mostly affects their ability to keep developing the non open source parts anyway, their SaaS dashboard, their billing, etc.
Take redis, you could never change it again and it's fine. There's no need to support anyone, it's complete software that stands on its own.
