Last October, Google revamped its Google Webmaster Guidelines into Google Search Essentials and one part of that was to consolidate the previous pages on thin content and affiliate programs into the overall documentation. Lizzi Sassman from Google explained a bit more on why this was done.
Lizzi said on Twitter, "the spam policy covers our current guidance on thin affiliates (hence the redirect)." "We simplified since some things are now covered by newer docs (ex: search essentials, creating helpful content, product reviews, etc) & aren't necessarily specific to affiliates," she added.
Lily Ray asked about this, and showed a screenshot of the archive of the old document:
the spam policy covers our current guidance on thin affiliates (hence the redirect). we simplified
— @[email protected] (@okaylizzi) January 13, 2023
since some things are now covered by newer docs (ex: search essentials, creating helpful content, product reviews, etc) & aren't necessarily specific to affiliates
Lizzi is saying that when Google reviewed the old documentation, they found there was no need to call out the affiliate aspect specifically. In short, it is not about a site being an affiliate but rather the tactics used for SEO purposes.
Forum discussion at Twitter.