In cases like HPC and other performance-centric workloads, mainline kernel just doesn't have the hardware support needed for more exotic stuff like Infiniband and Mellanox cards, high-end SSD etc. Oracle got tired of waiting for sufficient support to be included which is why IIRC OEL UEK was created.
If such hardware isn't being used, then yes, sanity should be questioned for supporting Uncle Larry's Linux.
