Most kernels not written in low-level languages (C, stripped-down unsafe C++, or assembly) were written for special hardware. Such hardware was built to handle

Most kernels not written in low-level languages (C, stripped-down unsafe C++, or assembly) were written for special hardware. Such hardware was built to handle a lot of the low-level details so that the software didn't have to. This particular approach can't be translated by software alone to modern general-purpose microprocessor-based platforms. Even if we were able to transition to such a do-more-work-in-hardware platform somehow, then we would just be trading kernel bugs for hardware bugs, and the latter aren't always fixable (even with firmware and microcode).