Because those are commodity processors nonetheless. The distinction relevant for a research paper is between mainstream processors you can just buy vs. custom made ones, not about market penetration.
> In economics, a commodity is an economic good or service that has full or substantial fungibility: that is, the market treats instances of the good as equivalent or nearly so with no regard to who produced them.
Basically it's a common good, that is sold and purchased, with no other modifications required for this use-case. This commodity is currently low in supply, but is still a commodity.
I think hard drives, memory, power supplies are much closer to being fungible.