Is that really so widespread though? All of my open source contributions were done on the job, fixing a bug or adding a feature to an open source project I use

Is that really so widespread though? All of my open source contributions were done on the job, fixing a bug or adding a feature to an open source project I use at work. There is a strong incentive to improve the project rather than fork it to fix, as you don't have to keep maintaining it yourself. It also appears that many maintainers are doing so as part of their duties at work. Just as Google maintains their search engine for "free" to show you ads, they maintain Kubernetes so that you use it on their cloud platform. You fix bugs in Kubernetes so you can have the fix you need, at work, when you need it.