The key reason for doing this, as stated in the article:
ultimately they say "the straw that broke the camel's back" to abandon Red Hat Enterprise Linux for their industrial accelerator-control computers was the "-march=x86-64-v2" compiler flag default as "forced obsolescence" for old hardware.
From what I understand, the v2 option requires relatively newer CPU instruction sets, making it incompatible with some older CPUs, even 64 bit ones. I don't know what is gained by using the v2 flag, but I would imagine that it may be something performance-related, by more fully utilizing those newer instruction sets.