Nobody gave you the actual answer. IBM was under an antitrust decree and had to openly license their technology for a nominal fee. (Supposedly about $5/PC.) So yes, they were in a hurry and used generic parts, but they still had tons of patents on it. When they got out from under this, they came up with Microchannel.

You're getting a lot of indirect responses. If you've ever tried to mod your android phone the answer is simple. Its google play services and hardware attestation for things like banking websites.

Its really easy to make a custom rom but hard to do serious "real life" stuff; companies don't want to make it easy. To most regular users, if they cant download apps from the google play store, and they can't use venmo\cashapp, then the OS is dead in the water from day 1

> Why are there not yet a plethora of phones on the market that allow anyone to install their OS of choice?

There are technical reasons, but as ever the real underlying causes are incentives. Companies realized that the OS is a profit center, something they can use to influence user behavior to their benefit. Before the goal was to be a hardware company and offer the best hardware possible for cost. Now the goal is to own as large a slice of your life as possible. It's more of a social shift than a technological one. So why would a company, in this new environment, invest resources in making their hardware compatible with competing software environments? They'd be undercutting themselves.

That's not to say that attempts to build interoperability don't exist, just that they happen due to what are essentially activist efforts, the human factor, acting in spite of and against market forces. That doesn't tend to win out, except (rarely) in the political realm.

i.e. if you want interoperable mobile hardware you need a law, the market's not going to save you one this one.

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”.

> 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

IBM didn't think to lock it down, the BIOS was the main blocker and was relatively quickly reverse-engineered (properly, not by copying over the BIOS source IBM had included in the reference manual). They tried to fix some with the MCA bus of the PS/2 but that flopped.

> almost every phone has closed drivers

Lots of hardware manufacturers refuse to provide anything else and balk at the idea of open drivers. And reverse engineering drivers is either not worth the hassle for the manufacturer or a risk of being sued.

> Why are there not yet a plethora of phones on the market that allow anyone to install their OS of choice?

Incentive. Specifically its complete lack of existence.

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)

Other companies saw that IBM effectively lost control over their platform (and thus lost a large revenue stream), and are determined to not make the same mistake.

That's a long running effort, going all the way from lobbying (DMCA and their ilk), to all kinds of hardware root-of-trust, encrypted and signed firmware, OS kernels and drivers etc etc. And yes, today we have the transistor budgets to spend on things like this, which wasn't an option back when the PC architecture was devised.

The hardware was evolving way faster 40 years ago and in much consequent ways than these days. Plus number of users grew exponentially. So a company spending too much efforts on software could loose its edge on the hardware side. And locking hardware would be counterproductive since as it would limit new users.

These days things are way slower and the are no exponential growth in users. Plus fast cellular networks made the speed of local hardware much less relevant. So the software became way more important and so its control.

The systems and software were vastly less complex and powerful in the 8088 days.

Very little of it was open, including the headliner apps of WordPerfect and 123.

Google had the benefit of three decades to study IBM's loss of control to prevent it with Android. Aside from China, they have been largely successful.

Because the original IBM PC was designed to be cheap and built in a hurry. IBM had a mandate for the original PC to use off the shelf components as much as possible. They also neglected to secure an exclusive license from Microsoft for DOS. 95% of building an IBM PC clone was buying the same parts and getting a DOS license from Microsoft (which they were very happy to sell you). Everyone saw what happened to IBM and just didn't do it that way again.

The business world learned from their mistake.

The company making a device that is licensed by the FCC has to do everything that they can to mitigate the risk of an unlicensed broadcast on their devices.

https://www.fcc.gov/oet/ea/rfdevice

> INTENTIONAL RADIATORS (Part 15, Subparts C through F and H)

> An intentional radiator (defined in Section 15.3 (o)) is a device that intentionally generates and emits radio frequency energy by radiation or induction that may be operated without an individual license.

> Examples include: wireless garage door openers, wireless microphones, RF universal remote control devices, cordless telephones, wireless alarm systems, Wi-Fi transmitters, and Bluetooth radio devices.

https://www.ecfr.gov/current/title-47/chapter-I/subchapter-A...

Other countries have similar regulations.

PCs don't have that restriction.

You might be able to get to the point where you have a broadcast license and can get approved to transmit in the cellphone radio spectrum and get FCC approval for doing so with your device... but if you were to distribute it and someone else was easily able to modify it who wasn't licensed and made it into a jammer you would also be liable.

The scale that the cellphone companies work at such liability is not something that they are comfortable with. So the devices they sell are locked down as hard as they can to make it clear that if someone was to modify a device they were selling it wasn't something that they intended or made easy.