PC was an anomaly thanks to IBM not being able to go with their plans.
On UNIX, Sun was the vendor that introduced the concept of SDK SKU, thus for having developer tools, an additional SKU had to be bought, and the until then largely ignored GCC sundenly got a new focus of attention.
Mainframes and micros always needed having a group of folks from the vendor professional services for specific kinds of configurations.
I still remeber working on traditional timesharing UNIX systems, one single server for all teams, what you get to do is decided by IT for your role.
There are plenty of examples from the past on how this has been happening already.
An anomaly from some corporate pov, maybe, but at home the PC was definitely not more open to general purpose computing than the alternatives. Most early home computers booted straight into a BASIC prompt, and the line between being a programmer and a user was far more blurred than it is now.
PCs from IBM could do this as well. There was a ROM'd BASIC in IBM computers that they would default to if they couldn't find a bootable disk. The BASIC that came with PC-DOS, BASICA.COM, was actually a wrapper for this ROM BASIC.
The clones relied on GW-BASIC and later QBasic, which came on disk and was bundled with DOS, to supply this functionality, and didn't have BASIC in ROM. In fact, some early BIOS implementations, if they did not find a bootable disk, displayed a message "NO BASIC FOUND" or similar.
But the "walled garden" on mobile (iOS mostly, but now also Android) isn't really about trusted computing at all. Trusted computing (locked bootloaders) is but a small part of it.
Trusted computing and even remote attestation have legitimate use cases. It's good, great even, that they exist. But just like everything, they can be used against you.
In fact most digital goods that are sold in large numbers via download, are, as far as I'm aware, sold with some form of DRM. Like films and video games. Otherwise piracy would be just too easy. MP3s don't have DRMs, and are still sold (e.g. by Amazon), but those now seem to be largely replaced by music subscription services.
And this might be a reaction to the fact that music piracy is quite easy; if it wasn't, perhaps there would be no Spotify where you get basically All The Music in existence for peanuts. (Note that no equivalent subscription service exists with regards to movies or games: Netflix and Xbox Game Pass have only a limited selection of content included in their subscription.)
