Both Single System Image and giant NUMA machines were and are still pursued because not everything scales in shared-nothing message passing well (some stuff str

Both Single System Image and giant NUMA machines were and are still pursued because not everything scales in shared-nothing message passing well (some stuff straddles it by doing distributed shared memory over MPI but using it mostly for synchronisation). It's just that there's a range of very well paying problems that scale quite well in message passing systems, and this means that even if your problem scales very badly on them, you might have easier time brute forcing the task on larger but inefficient supercomputer rather than getting funding for smaller more efficient one that fits your problems better.