fpga - Why is open hardware so rare?

I'm trying to understand why open hardware is so much harder to come by than software. I've tried looking around online and I couldn't find as satisfactory explanation.

I understand that hardware is so much easier to keep proprietary and so much harder (impossible) to reverse engineer (in the case of ICs, not PCBs), but why would that hold back open hardware initiatives?

Is it the cost of manufacturing? Is it the lack of shared knowledge about hardware design? Is it the complexity involved?

With the advent of FPGAs making it so easy to design hardware (although they themselves are proprietary as well), I would expect that open hardware would be taking off at a much faster rate than it has been.

I'm sorry if this is the wrong place to ask, but this has been perplexing me for about a year now and has made me wish I had taken Computer Science instead of Computer Engineering.

Answer

Everyone can edit source code at home, very few people have a chip fabrication plant to knock out a couple of custom chips. Bytes are free to create and distribute, materials are not.

There's also the issue that source code is portable, and although CAD files etc. are sort of portable, there's a lot more overhead & errors & setup cost wasted materials.

3D printing crosses some of the boundaries, perhaps a bit of effort could do the same for the (much older) technology of machining, both parts & PCB's.

Edited to add: re-reading the question, and perhaps the intent of the question relating to FPGA's, I would say that they're currently still a bit of a dark art to many, and just not on the radar of most people. The entry barrier is quite high, in terms of effort, understanding, and tools.