(( I've split my reply into three parts to avoid a wall of text in a single comment.

I may run into "you're posting too fast, so not all part may appear at the same time" ))

Part 1.

> I honestly believe that 90% of the dislike for WC comes from the name "connectedCallback". If they'd named it "onCreate" or something, everyone would be using it

Of course not. None of the criticism towards Web Components ever mentions "connectedCallback", or how it should be named differently.

Do you know the actual reason so few are using them? Let's skip the atrocious not-really-high-level not-really-low-level imperative API that they offer.

How about:

- 13 years after introduction they still need 20 more specs to try and patch just some of the holes in their original design: https://w3c.github.io/webcomponents-cg/2022.html

- Shadow DOM is infecting every spec so that the actual useful specs like Scoped CSS have to be delayed almost indefinitely to try and figure out how to work with this abomination of a design

To quote the report linked above, "many of these pain points are directly related to Shadow DOM's encapsulation"

- The amount of specs that are required to make them work, barely, and be "good web citizens". And the amount of APIs.

Oh, you want your custom input to a) be able to send its data in a form, and b) be accessible to a label outside of your component? Well, there's a separate API for a) and there's some separate future API for b). And meanwhile your custom button won't be able to submit your form, sorry, it's a 4-year old issue with no solution: https://github.com/WICG/webcomponents/issues/814

And all that despite the fact that there are already a dozen specs covering web components, and dozens more on their way.

- Web Components ar HTMLElement. It means you cannot use them inside SVGs.

This is impossible:

    <svg>
      <x-axis min="2000" max="2019"/>
      <y-axis min="0" max="100"/>
      <scatter-plot points="..."/>
    </svg>

This makes them unsuitable to a huge swath of graphics- and visualisation-related applications.

- A smattering of other issues:

-- They cannot be easily used when progressive enhancement is required: SSR story is still non-existent, you can't easily update the original DOM in a custom element without trashing it.

-- They cannot be easily lazy-loaded because slotted content is eagerly loaded:

    <p>Toggle the section for more info:</p>
    <toggled-section>
      <html-include src="./more-info.html"/>
    </toggled-section>

`html-include` will load in its entirety even if you never toggle the section. And yes, this causes a cascading loading of multiple resources, too.

-- they share a flat global namespace. Of course this will be solved in the next five years by a yet another spec.

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If any userland framework had these many issues, it would be laughed out of the room. And yet here we are with people trying to argue that they are good now actually and all that stops them from being used is "connectedCallback" name.

These are also the reason why most framework authors that initially supported web components (Vue, Svelte, Solid) are now at best completely indifferent towards them.