It's a term coined by Cory Doctorow, Sci-Fi writer and ex-EFF, who has been writing about (tech) monopolies, and in particular monopsonies, and how those types of two sided markets originally grow by given users something they need, often for an artificial low price or even free, until they dominate that side of the market, after which they focus mostly on the other side of the market, in this case advertisers, and step by step, slowly dismantling the reason users originally liked their product... Enshittification.
Now that the concept has caught on so widely, I've often wished @pluralistic@mamot.fr had gone with a less scatological term. But maybe that is part of the reason it caught on 🤷🏻♀️
There is some perception bias there, because you won't hear that much from people who don't want to use the term (like me), unless they engage in a pointless meta-comment like this one.