edit: speaking mostly about macOS here, mobile OSes are much more locked down
It was only really open to ease the transition between intel and arm.
You can’t have a development machine locked down like iOS. As long as the Mac is the development machine at apple it will need to be able to run arbitrary code.
But they'll remove support for other OS's
Made the laptop miserable to use, so I went for a MacBook instead which wouldn't have such an obvious issue be unfixed because Apple has so few SKUs to support.
Also went for it in part because I do not like Windows and macOS typically would save me when Linux support was lacking. Just had to hope for a quick port of Asahi Linux to become (unfortunately didn't happen for my M3, but thankfully it's been progressing recently).