True. However, sometimes large buyers, such as governments or enterprises, change their policies towards purchasing requirements. For example, since 2013 France has had an Inter-Ministry Foundation of Free Software[0], which provides the preferred software to be used across France's government, as French law requires preference be given to free software (logiciel libre).

What impact might occur if a government like France were to require in the future only RISC V architectures with free boot loaders, of if the US government or a large corporation required use of measured boot to see at boot-time if the boot code or subsequent OS had been compromised?

With persistent threat actors and the falling price of processing power, I wouldn't be surprised if in the next ten years some larger organizations (or tens of thousands of small businesses) start demanding this kind if IT security from their vendors.

[0] (in French, of course) https://sill.etalab.gouv.fr/fr/software and their repo, https://github.com/disic/sill.