Many developers work on FOSS for free. A project with a good community often has many people who contribute the occasional bug report, patch, or documentation a

Many developers work on FOSS for free. A project with a good community often has many people who contribute the occasional bug report, patch, or documentation addition. Few developers work on FOSS full time for free, at least for very long. However, there is a sizeable group of FOSS developers who do full time or large amounts of part time work for far less than market rate, especially those who are funded primarily through donations. You can go to many smaller projects and see the level of donations they get (e.g. the creators of Godot pay themselves $4400/month, and that is one of the most financially successful small open source projects). I would suspect even for the projects you mentioned above, money is far from the primary motivation of the developers, and they could make more elsewhere.