Hardware support is also one of the reasons to keep using OS9. I still use it on a 1998 Powermac almost every week as my drum scanner requires a custom PCI card

Hardware support is also one of the reasons to keep using OS9. I still use it on a 1998 Powermac almost every week as my drum scanner requires a custom PCI card and an app that ties everything together. Its vendor went under long ago and so no one to port their app to OSX. Works like a charm, with original keyboard and mouse.