Firstly, let's assume you basically need a big company to opensource their existing IP because opensource is no where near where Intel is today. So let's look at the obvious choice: Intel has traditionally perceived itself to be a manufacturing company. It tries to produce as many chip widgets as possible and producing CPUs or SSDs or network chips is just their way of finding ways to sell their widgets. The core of their business is fabrication.
Now, the only companies they let use their foundries to produce other chips are almost exclusively companies that they end up buying (I'm looking at you Altera).
By open sourcing their CPU designs they are practically guaranteeing that some of the chips they produce today would be produced by Samsung and TSMC. Try explaining to their share holders that you're giving away the crown jewels, damaging the core of the business and hoping for what....?
Secondly, taping out a chip is hundreds of thousands of dollars. Even if you did opensource everything, the only people who could actually produce the chip would be huge corporations, and the process of taping out isn't "Let's save it to a floppy and send it off". All of the tape out process requires proprietary tools from the fab, which are only available to the serious customers. So your source might be open but no one outside the company would be able to actually read them. And this is non-trivial, TSMC consider their tools to be a core part of the IP that differentiates them, they'll never release them under anything but a very strict contract to a client.
Finally, one of the key benefits to opensource is that you can fix something yourself, you can contribute and change things. Well not in hardware. The best you can manage is to fix the problem in the next $X00k production run.
Laying all that aside: No one has actually described what benefits Open Source software has over closed source that we're trying to map to hardware? To me a key benefit of Open Source is that we don't depend on corporations as gatekeepers to fix things, well that isn't solved in hardware open source.