In the space of such foundational technologies, there’s always been a vast gap between the number of private vs open-source projects that succeed. Even all the way back to proprietary compilers 40-50 years ago.
If they had stuck to being an open-source project, the kind of adoption and mindshare they achieved would have put them among the most successful ever. And I am sure they would have been able get their team paid very well sustainably. The unicorn model cannot fit every single venture.