very hacky syntax embedded into html. Sometimes you had to even use some kind of comment notation because there was no entry point into the html to add data properties or whatever it had.

it was slow.

the observables weren't variables you could use like plain JavaScript variables

it has the same problem as React - state-based algorithms are not very good ways to solve problems (if (showDialog && !open && ranOnce). You have to keep creating more variables to represent more states instead of using normal programming language concepts, and then all of the observables ping around and become complicated.

Angular had a "made by google" kind of logo on its website, indicating to many people that it's of high quality and worth adopting.

But Angular was also so convoluted and had so many problems that so many people kept running into random problems all the time and had to ask questions about them on SO. This signals (incorrectly) that Angular is popular, driving more people to believe it's worthwhile to adopt it.

Knockout had neither. It was not sponsored by a corporation. And it was so good that you hardly ever run into random problems.

Ultimately it was eclipsed by React and Typescript because lack of type checking for the html templates means it's hard to scale it will to large projects.