The whole idea of web components was somehow sold inside Google, hard. They even re-wrote Youtube with web components v0 which was almost immediately deprecated. And Chrome had to support it for years before Youtube rewrote stuff in v1.
Since then Google has abandoned Polymer and now has a new toy called lit-html. And is now busy writing stuff in lit-html.
Last year they shipped Constructible Stylesheets by default in Chrome despite the fact that both Safari and Mozilla were against the state of the spec and the proposed implementation.
The only reason? lit-html was going to use it. And the justification for not hiding it back behind the flag? "Oh, our internal metrics show 0.8% of sites using them", which, at the time, was exclusively Google-developed lit-html exclusively on Google-developed properties.