People/projects can and do implement userspace networking stacks. For example, gVisor implements its own userspace networking stack [1] isolated from the kernel

People/projects can and do implement userspace networking stacks. For example, gVisor implements its own userspace networking stack [1] isolated from the kernel networking stack. [1]: https://gvisor.dev/docs/user_guide/networking/ https://gvisor.dev/docs/user_guide/networking/