As far as I could tell, around that time (and even now to some extent) the amount of activity on StackOverflow is used to measure the popularity of a project.

As far as I could tell, around that time (and even now to some extent) the amount of activity on StackOverflow is used to measure the popularity of a project. 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.