Basically, it's the theory that capitalist economies demand continually increasing growth, even increasing rates of growth, in order to remain stable enough to stay hegemonic. The industrial revolution, through most of the 20th century, exhibited this growth, driving capitalism to be the dominant (eventually only) economic system on earth.
Unfortunately, growth is hard, and it slows down. Over time, providing meaningful improvements to the lives of the participants in the economic system fails to keep up with the demands of growth, and you start to see the system going full ouroboros, consuming all the positive impact its created in the lives of its participants in a downward spiral of exploitation and value extraction until there's nothing left. The period of time after the inversion from "making people's lives better" to "making people's lives worse" is "late-stage capitalism", equivocating it to cancer or other terminal diseases.
Personally, I'm more of a "threshold events" theorist, and that enshittification is just reversion to the mean, but that's the pitch.
Unfortunately, growth is hard, and it slows down. Over time, providing meaningful improvements to the lives of the participants in the economic system fails to keep up with the demands of growth, and you start to see the system going full ouroboros, consuming all the positive impact its created in the lives of its participants in a downward spiral of exploitation and value extraction until there's nothing left. The period of time after the inversion from "making people's lives better" to "making people's lives worse" is "late-stage capitalism", equivocating it to cancer or other terminal diseases.
Personally, I'm more of a "threshold events" theorist, and that enshittification is just reversion to the mean, but that's the pitch.