> is considered more stable

Was not stated.

> Why shouldn’t they use stable technology they are proficient with?

This perspective is one of the major indicators of an engineer with more experience managing real projects. Making a technology choice or transition is a milestone/roadmap affecting decision. To do so for preference over deliverability has killed many a project.

Despite all the talk, there isn’t a world of difference between how apps used to be written 10 years ago and more modern frameworks. The tooling and the language have evolved, but you still manage state in similar ways, fetch data, build components, render.

Mainly you’ll be managing the rendering lifecycle manually in Backbone, which you’d end up doing in React anyway to get the best performance for an app like this - you’ll get molasses if you naively build a spreadsheet in react.

One thing I consider a huge advantage: you can read and understand the source in one afternoon. Makes debugging and optimization a lot easier.

Well, think about it like this. React had several major versions in recent years, and did remove several APIs. Also the whole thing with the new hotness of the hooks API (which, honestly, I just truly don't get).

Angular had the whole thing with Angular 2, where they just shipped a whole new framework with the same name. So everyone with angular 1 codebase was, well, stuck with angular 1.

Don't know much about vue, but I think there was some drama about rather large API changes from Vue 2 to Vue 3. Correct me, if I'm wrong.

Backbone and Knockout, on the other hand, look fairly complete. Almost no chance of backwards incompatible changes there. So you can just write your code and be done with it.

But, honestly, one should use things that one knows. My current project is written in React. I'm fine with it. And if I had to start a greenfield one, I wouldn't use anything else, because I am proficient with React. I can deliver features. After all, our customers want the features, not the hot new framework.