It’s not exactly new. Pig slop is generally random food scraps etc. Big brother used “slop” for their flavorless penalty food long before LLM’s.

Arguably the connotation has changed slightly, but AI slop caught on because it fit so well.

"slop" is a type of British food (like "Gruel").

It's uncommon, and associated with old timey prisons and orphanages.

The word itself has existed for hundreds of years.

Slop is also evocative of spam, another great unwanted gastronimic tech byproduct.