You write as if we didn't understand the technical value of those things before a couple of years ago when the current crop of JS frameworks arrived, and as if using one of those frameworks is somehow necessary to achieve them.

In reality, everything you mentioned has been widespread in other software development fields for decades. It's stuff the junior guy on the team learns in his first few months.

Moreover, I think there is a reasonable argument that of your chosen examples, testing is the only one that has sufficiently common requirements for building large but general tools to be worthwhile. The other design principles are valuable, but how best to use them will be highly project-specific, and therefore any widely useful framework will tend to be over-engineered and over-generalised for most applications. See also the Java nightmare I mentioned previously, the trend toward lightweight frameworks on the server side, etc.

Edited to add:

The myth that front-end developers are not "necessarily from a programming background" is poisonous thinking and it unfortunately usually comes from older programmers or non-front-end developers; the very people who could help guide the front-end world into maturity.

There is a difficulty in the industry that significant numbers of people are coming into this kind of front-end development from some sort of HTML/CSS and/or design background. They used to use a bit of JS here and there that they copied off a demo site to get their buttons to animate, and now they're being asked to move into more of a mainstream programming role, but neither they nor the people asking them necessarily appreciate what that involves.

That's not anyone's fault. It will be fixed over time as the industry matures, both because knowledge will spread and because more specialised roles than "front end developer" will probably evolve. But right now, today, it is the situation in large parts of the industry.