Cray just won a $600M bid for Oak Ridge National Labs' new exaflop HPC cluster using AMD Epyc/Radeon.
Most IB cards come from Intel and Mellanox (recently purchased by NVidia).
IB is a commodity, sure, but it's becoming increasingly tied into the Intel/NVidia ecosystem, and having the ability to go with another interconnect/processor architecture is a powerful strategic advantage.