This is a deceptively insightful comment. At least it wasn't clear to me for a while.
If you want to start a business it can definitely have an open-source element to it, but that's just it. The open-source part is just one piece to a business and you better be aware of all the other pieces that need to be done in order to make money which aren't always engineering/programming related. EG: marketing, sales, consulting, fundraising, accounting, etc...
A common approach that people do now is create the open source offering then run it as a service where they can charge a premium for the support and leg work for hosting it. See: mongodb or elasticsearch or influxdb.
I haven't found many pure open source solutions where all they do is make the software better all day and ignore all the elements of business growth needed. Maybe the Linux foundation is a good counter example but I don't think there is a clear path to be paid for just contributing solely to open-source while neglecting other business elements.