GrapheneOS is the only Android OS providing full security patches

Why was it that in the early PC days, IBM was unable to keep a lid on 'IBM compatible', allowing for the PC interoperability explosion, yet today, almost every phone has closed drivers, closed and locked bootloaders, and almost complete corporate control over our devices? Why are there not yet a plethora of phones on the market that allow anyone to install their OS of choice?

Cory Doctorow answers this in his book “The Internet Con”. IBM fought with DoJ for years. Today, it’s a felony to mess with anything locked down (anti circumvention)

I don't think it's a felony to root/jailbreak one's own phone.

It is. 17 U.S. Code § 1201 - Circumvention of copyright protection systems

Well actually, it isn’t for individuals and certain groups, technically.

Rooting/jailbreaking have had exemptions for many years now, on a three year basis which has seemingly been continually renewed, by the Librarian of Congress.

Exemption to Prohibition on Circumvention of Copyright Protection Systems for Access Control Technologies (2024)

https://www.federalregister.gov/documents/2024/10/28/2024-24...

https://www.eff.org/issues/dmca-rulemaking