Why do we need Docker, virtualization technologies?
Because popular kernels are bulky, badly designed and don't provide the virtualization facilities we need.

I think a proper OS kernel should at least have these properties:

1) An OS kernel must not have any driver code for external devices. External devices should describe themselves.

2) An OS kernel source code line count must be in thousands, not millions. Only absolutely necessary code should be there. (isolation, protection...)

3) An OS kernel must provide its isolation, protection, resource management etc. source code as reusable libraries for user-level applications.

27+ Million lines of code in the Linux kernel [R0].
We should stop and think about what 'kernel' means.
I think of seed or atomic nucleus when I see the word kernel.

Operating system kernel lines of code should be fewer than one million (it should be a couple thousand at max). Drivers don't belong in kernel.

OS kernel should do only the most fundamental tasks (resource management, resource security etc.) and provide facilities to other programs, devices.

The C language should not be used unless it's absolutely necessary. A programming language like Rust must be used to create secure, formally provable software.

R0 ; (January 7, 2020): https://www.linux.com/news/linux-in-2020-27-8-million-lines-of-code-in-the-kernel-1-3-million-in-systemd/