querySelector() and querySelectorAll() are similar to jQuery, but they are not what unseated jQuery. It took a new library with compelling new features (unidirectional data flow, no need to use a special, crippled language just for templates) to get people to abandon jQuery.

React is the dominant client-side web framework, but its preferred template syntax has a method for inserting components into the document which is totally different from the "standard" (and Ember) way of doing things. JSX uses CapitalizedComponentNames, while the standard uses dasherized-component-names. JSX has self-closing tags with slashes before the closing angle bracket, while the standard does not.

There are perhaps tens of thousands of devs using React, Preact, and Inferno. How can these differences be smoothed over in order to enable universal web components?

I do when they work. I really hate when someone reimplements select without supporting things like typing to skip select an option. And honestly, on mobile, the built ins are the best.

There are react components that provide a good experience that replicates the features of most built ins, but it's a constantly moving target considering native widgets vary between platforms.

In general I agree with you and gp though. I would love for web components to one day be the standard but I'll believe it when I see it.