Right, you cut to the heart of things. There is a licensing "race to the bottom" happening. Which makes sense from the demand side (of course people want free). But where does the supply side come from?

Why does the floor keep constantly dropping? Who are these developers, always willing to do more for less?

In my experience:

* Some of it: people who open source their hobby projects. The personal upside of investing resources into open source is fun & practice.

* A lot of it: academia. Universities have an infinite supply of indentured labour in students and postgrads. The personal upside is grades and graduation. The institutional upside is publishing and grant money.

* Lately: large enterprises. These have the resources to throw high quality engineering behind their open source projects (unlike the universities, where quality has always been a struggle, due to tremendous "developer" churn and different incentives). The personal upside is salary; the business upside is $$$ via "commoditize your complements". Added bonus: open source serves as an HR tactic too.

Put together, the demand for the "race to the bottom" is there and so is the supply. And so it happens. The machinery behind "If you don't do it (with a permissive license), someone else will".