"all these Linux servers in the nearby server plant"
The servers built by manufacturers who think Windows compatibility matters (Dell, some bits of HP, whitebox vendors like Supermicro) are based on x86, and historically it has been convenient to use them for Linux too.
The servers built by manufacturers whose business is not Windows dependent because they use some other OS (a genuine UNIX, a mainframe OS, VMS, NSK, whatever) - how many of them choose x86? Look around. Show me the answer is bigger than zero.
Actually, Michael B. already did and pointed out the Top 500 Supercomputers list.
Historically, and presumably still currently, the presence or absence of a particular product in the Top 500 is quite likely to reflect the availability of vendor funding as much as it reflects other criteria generally more relevant in the outside world. Work out what that means. Then tell readers why it matters anywhere outside the supercomputer market.