[regularfry]

"Valuable product maintained by professionals" doesn't equal "proprietary". All those products you list have people paid to work on them.

Open Source doesn't work in the long term without sponsorship of some sort.

[EugeneOZ]

You want to say these products are not valuable or not maintaned by professionals? They are making money around their projects same as RethinkDB did, so I don't understand what difference you want to underline.

[disordinary]

Plenty of software companies build their businesses around opensource software and pay their employees well. The list is endless