linuxkpi

I was looking at the linuxkpi source code in /sys/compat/linuxkpi and I had
a question.

A lot of those files just look like linux files brought over to FreeBSD, is
there any reason why those files couldn't be implemented in BSD w/o the
dependencies on the other Linux headers?

For example this header file:
sys/compat/linuxkpi/common/include/linux/workqueue.h

the workqueue.h, there doesn't seem to be anything special in there that
couldn't be implemented in BSD without relying on the Linux import
statements.

Maybe I'm missing something but why can't these files and functions be
implemented directly with their BSD equivalents?

Best,
Owen