> The web browser isn't Netflix trying to serve hundreds of gigabits per second of encrypted video streams from a single server.

Ironically, server workloads are the ones that are increasingly moving to networking stacks that run in user space, using frameworks like DPDK, with performance as a motivator: https://en.wikipedia.org/wiki/Data_Plane_Development_Kit

Of course, there are some caveats - from my understanding, typical DPDK use cases would turn over the entire NIC to a single application, meaning you aren't contending with sharing the network between multiple, potentially adversarial user mode processes. This is fine for a server, but not really appropriate for a PC or smartphone.