[Kwpolska]

Apple used to sell Macs with Intel (integrated), AMD, and Nvidia GPUs. In other departments, they also had multiple vendors and chips. The Apple Silicon transition streamlined the product lines, but before, there were tons of drivers, and macOS had to support all of them for 5+ years after the product release.

[memsom]

They were still in complete control of the platform though. You couldn't just take a OS build and put it on another generic computer without a lot of hacking and/or picking hardware as close to the actual hardware that the OS could handle the differences. I know people did it - heck I had a hackintosh netbook back in the day, but it was not a trivial process and someone had to have done the work already for the "Average" consumer.