High performance implementations, i.e. actual chips you can buy, are going to be proprietary and that's not going to change. Engineering hardware is expensive.
But there are different levels of proprietary. Having your entire software ecosystem impossible to lock-in means something. And competition tends to breed openness.
MIPS certainly did gain a lot of traction. It was a real force at one point and the world is awash in them. But of course MIPS (the company) is RISC-V now.
A cutting edge processor requires personnel across several disciplines and millions in specialized equipment to both validate the implementation of the architecture and the electrical behavior of the circuits and each time it's "compiled" (a batch of test chips fabbed and QAed), it takes a few weeks to be delivered and costs hundreds of thousands of dollars. The ISA being open and royalty-free doesn't affect any of those massive costs.
To use a famous quote: "The answer to any question starting, 'Why don't they...' is almost always, 'Money'" Nobody is offering up that kind of money without practical guarantees of success and some kind of profit at the end of it.
The Linux kernel may be "free" but it represents millions of man hours (or years) of engineering. Creating a viable RISC-V chip would be easier.
Creating the AV2 video codec cost money. I assure you. There is a reason that the Alliance for Open Media is a list of Fortune 500 companies and not a bunch of individual developers.
I have worked in industries dominated by a single chip supplier that made the chips that everybody used. Video surveillance is a good example. It would have been much cheaper for the major players in that industry to fund the collaborative development of chips they could all use and that could maybe be "tweaked" to add differentiated value for the largest players. It would save them money. It would give them more control (even more valuable).
I assume you know what a "chiplet" is. RISC-V is going to change things. In my view, you are focused on the wrong constraints.
We are both saying that money matters. We are simply coming to different conclusions about what that means.
