I am not sure if you are referring to the runQueue being used in Linux or the whole approach. I try to answer both:
Run queues can be part of any scheduler, they are queues with runnable tasks.
But as why the approach is worth while in user space, it has to do with low cost of operations (context switches) in user space, and also using cooperative scheduling instead of preemptive. Cooperative scheduling provides more control to the user over the tasks, and also has lower overhead since there is no need to manage a quantum for each taks (thread).
Run queues can be part of any scheduler, they are queues with runnable tasks.
But as why the approach is worth while in user space, it has to do with low cost of operations (context switches) in user space, and also using cooperative scheduling instead of preemptive. Cooperative scheduling provides more control to the user over the tasks, and also has lower overhead since there is no need to manage a quantum for each taks (thread).