Perhaps they would want all of those cores on one motherboard.....

Not to mention the hundreds of PSU's and sticks of RAM for each motherboard you buy.

I think people need a reminder that this is enterprise server hardware, so though this may be expensive (even for servers), it's not outrageously so. I have worked on a single computer that was worth $3 million. Regardless, it doesn't seem like a wise choice to buy. For anything massively parallel, GPUs are better. ARM is better when you want many individual small tasks.