This, exactly. Rosetta 2 emulates x86_64 Darwin binaries on AArch64 Darwin - it means that tricks like jumping to native code as soon as possible are feasible.
For instance, you can call a native counterpart of a system library instead of emulating it down to the syscall level, and generate native code that calls into that.
Running kernel level code requires you to emulate an entire machine, which is way more complicated than just emulating the userland like Rosetta does. Running an unmodified OS kernel requires emulation of stuff like interrupts, firmware, peripherals ... Yes, you can dynamically JIT compile some codepaths into native code, which is something that AFAIK most emulator already do, but there's still a much higher performance cap than with something like Rosetta or Wine.
For instance, you can call a native counterpart of a system library instead of emulating it down to the syscall level, and generate native code that calls into that.
Running kernel level code requires you to emulate an entire machine, which is way more complicated than just emulating the userland like Rosetta does. Running an unmodified OS kernel requires emulation of stuff like interrupts, firmware, peripherals ... Yes, you can dynamically JIT compile some codepaths into native code, which is something that AFAIK most emulator already do, but there's still a much higher performance cap than with something like Rosetta or Wine.