Kubernetes was designed for Google-scale web services in 2013. Slurm dates back to 2003. Both are built on antiquated technology stacks that predate modern kernel capabilities — io_uring, eBPF, cgroups v2, idmapped mounts — none of which they can take advantage of without layers of bolt-on complexity.
Most teams don't run Google. But they're stuck with Google's decade-old tooling.