What people using web components want is to get rid of shadowDOM and not feel like they are deviating from the correct path. shadowDOM sucks, stop trying to convince the world that we are using it wrong. shadowDOM is the whole reason web components did not become mainstream (yet?).
Nothing in Web Components is forcing you to use ShadowDOM. Lit also allows you to make components without ShadowDOM if you prefer, because there are certainly cases where it can be necessary to do so (like for ARIA reference id-matching). For full single application development, it can feel like it gets in the way a lot, and you can make a good argument to use components without ShadowDOM in those contexts too.
All frontend "frameworks" do have some sort of solution to scope CSS to individual components, and without a similar solution, a native component system would not be viable. The implementation has its quirks, but it is a core capability that is necessary for some use cases. For third-party widgets or cross-application components like design systems, the ability to isolate your component from the site it is embedded in is very useful.
Think of shadowDOM as the web component alternative to scoped styles in Vue components (as an example). You don't have to use it, but it would be incredibly inconvenient if it wasn't included in the framework.
> Nothing in Web Components is forcing you to use ShadowDOM
Yes. There is just one thing forcing someone to use shadowDOM: slots. You can't use slots without shadowDOM or at least use something like this.children to capture the content inside the <custom-element></custom-element>.
It's not possible to make slots work without a separate tree like shadow DOM. The browser can't tell what the container for a slot is vs what content should project into it.
I disagree completely. Shadow DOM is a huge help and when combined with per-component CSS using the :host() and nesting pattern, makes for very small CSS files and very short CSS class names. In other words, as far away from Tailwind as you can get.
It's also possible to import shared CSS in a base class and add it with super.styles() so you don't lose anything.
You don't want to enable portable components all the time. If most of the components you use to create your app is made by yourself, those boundaries are annoying, not helpful.
What people using web components want is to get rid of shadowDOM and not feel like they are deviating from the correct path. shadowDOM sucks, stop trying to convince the world that we are using it wrong. shadowDOM is the whole reason web components did not become mainstream (yet?).