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?

The only thing proprietary in the early PC architecture was the BIOS. Everything else was pre-existing architecture from third parties, there was nothing to keep a lid on.

Since a PC was a big box of parts anyone could manufacture one. A modern phone is much more complicated.

As to why there aren’t a plethora: the market doesn’t demand it that much. The people doing it aren’t wildly successful. Perhaps that’s changing (I hope so) but I know very few people outside this community who have ever thought “I wish I could have a third party version of Android”.

Even the batteries are not interchangeable on phones. You'd think all phones should have the same exact battery, that this kind of standardization is beneficial for phone manufacturers as it helps them bargain with their parts suppliers but no for whatever reason we can't have that.

Edit: I am not saying just user replaceable. I mean standardized so the same cells in a 2024 phone also works on 2025...

Why, of all parts on a phone, would you expect the battery to be the one that's already good enough that it should never need to be upgraded?

"Battery capacity" is like the one thing phone manufacturers still try to improve.

The interfaces and the external dimensions can remain the same even as the internals change though, right? And you can have more or fewer cells. The cells don't have to be cylinders, either. They can be flat.