Apple has a long and storied history of pulling shit like this.
Back when Macs still had SCSI, Apple used a non-standard 25-pin connector on their desktops, and
whatever the fuck this was on their laptops. Classic Mac OS also refused to talk to any hard drive or CD-ROM drive that didn't have custom Apple firmware installed, something that only changed when OS X came out. Want to connect your shiny Mac to this fancy new ethernet thing?
Fuck you, buy our special dongles! By the time we got to the Powermac, you had to
buy dongles if you didn't want to replace your monitor, and Apple would repeat this move a decade later with
Apple Display Connector.
Mini-VGA and
Mini-DVI were also common on iBooks, PowerBooks, and MacBooks up until Apple started putting DisplayPort on Macbooks. Side note, apparently
Mini-DisplayPort is also an Apple invention, but that at least got some traction outside of Apple.
There was
this USB cable, designed specifically to prevent you from using non-Apple USB devices. FireWire may as well have been proprietary to Apple since they were the only company to ever include FireWire on their computers, and you only saw FireWire in the PC world if someone had a Sony camera - if you wanted digital video out of your camcorder, the only way to do it was through FireWire.
We could classify Thunderbolt the same way as well. If you wanted full gigabit ethernet on a Mac you had to
buy Apple's special dongle because Apple refused to put a USB 3.0 port on the Mac until USB-C came out. Nowadays Thunderbolt 3 and 4 were rolled into the USB-C spec so I guess it's not as proprietary anymore? Back when Macbooks still had replaceable storage, sure, the interface was NVME but the connector was completely proprietary.
That's why these adapters exist.
Special mention to the 30-pin dock connector. You'd think with the recent resurgence of old iPods that people would be making cool accessories for the 30-pin connector, right? I looked into it a while back - if you want to do anything more with the 30-pin connector besides transfer data and charge, good luck because the communications protocol is encrypted and nobody's ever leaked the spec or bothered to break the encryption. There's also the tiny little problem that you simply cannot buy the male connectors anymore. I looked high and low on every component distributor's website and even into the depths of AliExpress. Those connectors just don't exist anymore. And you can't just buy old USB cables to hack with because those are only pinned out for the four USB pins, not the full 30 pins the connector supports.