https://en.wikipedia.org/wiki/Regression_toward_the_mean

The way this works is:

1) x% of users have an exceptional first experience by chance. Nobody who has a meh first experience bothers to try a second time. 2) x²% of users also have an exceptional second experience by chance 3) So a lot of people with a great first experience think the model started off great and got suddenly worse

Suppose it's 25% that have a really great first experience. 25% of them have a great second experience too, but 75% of them see a sudden decline in quality and decide that it must be intentional. After the third experience this population gets bigger again.

So by pure chance and sampling biases you end up convincing a bunch of people that the model used to be great but has gotten worse, but a much smaller population of people who thought it was terrible but got better because most of them gave up early.

This is not in their heads- they really did see declining success. But they experienced it without any changes to the model at all.