you need a diversity of opinion in order to make meaningful progress and that is more likely to happen when there are different companies
Once the ones that are successful bear fruit, those that are working on the failures can be moved over to the successful groups. And instead of the current environment, where there is a lot of wasted effort allowing an inferior product to go all the way to market to languish there, the decision can be made much earlier than that, saving all those wasted resources.
I think it is a result of human nature responding to the incentives provided by their company, their education, and culture. Most people, if hired to lead the work on an idea, will become upset or stressed if they learn of another group at the company that is also focused on the same area.
Companies can adapt their culture and organizational model to create an ecosystem in which diverse efforts can develop at their natural pace. However if that was easy to do well then there would be no need for companies to hire external design agencies.
At the scale of chip manufacturers such as Intel and AMD they probably feel that they are considering many diverse opinions, but each company has its view and once they decide on the path forward they will cut any staff that are not contributing directly to that path (or at least AMD will.)
Your idea is appealing in basic theory, for sure, but a few thousand years of experiment and more sophisticated theory of actual human nature disproves it.