Because a kernel is the interface between applications and hardware resources. Modern microkernels are ~50% architecture dependent code. Creating a common int

Because a kernel is the interface between applications and hardware resources. Modern microkernels are ~50% architecture dependent code. Creating a common interface would require all OS vendors to collaborate on some standard and maintain a leaky abstraction over their preferred abstraction. You can do that, but there are feature, performance, and maintenance compromises that must be made.