It's true that the FPGA vendors are very secretive, often to the point of requiring NDAs for access to datasheets and toolchains. There is open source tooling

It's true that the FPGA vendors are very secretive, often to the point of requiring NDAs for access to datasheets and toolchains. There is open source tooling for some FPGAs and a fairly small but very helpful community around it. Yosys, IceStorm, SymbiFlow, and nmigen are the major projects in the space that I'm aware of.