This is similar to the rapid early adoption of the Bootstrap CSS framework. A lot of people were annoyed by the sudden spike of websites that looked and felt the same, but I think this was a tremendous step forward in usability and accessibility, and well worth the initial wave of cookie cutter websites.
The difference here is that the slop paradigm is not a set of intentionally designed UX choices that work well for users, it's a set of accidental commonplace LLM tendencies, not designed for humans, replicated ad infinitum that are making user experiences worse in 99% of cases. The use of white space is horrendous, the font choices are illegible, the color palettes lack sufficient contrast.