The problem isn't that developers "expect" this stuff to be free. It's that the quality of a particular development platform is related to how many people are using it - how many tutorials are there out there, how much sample code, how many libraries, etc.
There may be some social bias against paying for stuff, I think partially because people got burned with vendor lock-in. Technology changes so quickly, it's hard to know what a tool is worth before the fact.
But there's also a very real economic reality at play here. The most valuable platforms will be the ones with the most people collaborating on them, and that's always going to be the free or open platforms.
As you move up the infrastructure chain, I think people are more willing to pay for useful libraries or services, especially for ancillary stuff. But what rational person would build their business on something they didn't own?