People are reasonably expected to learn k8s or React on the job, and those have a learning curve as well. Are MPI/OpenMPI much more difficult than those? I suppose that's a hard comparison to make. At first glance it doesn't look too crazy to me.
MPI is trivial to learn. CS students here are expected to use it for typical scientific tasks within a few hours of lessons. Complex use cases take some time to understand backgrounds (e.g. multi partition configurations, profiling, infiniband, ...) and it's possible to become a specialist, but that's very rarely needed.
But MPI, in most use cases, comprises far less than React does, so it's not a fair comparison.
https://www.eecis.udel.edu/~youse/openmpi/#/7