Because it was pushed and is being pushed primarily by Google and its devrels. After 12 years in development they are barely usable, have a ton of issues that are not resolved [1] and [2], and any client library in the same state would be laughed out of the room by anyone.
However, there are now hundreds of millions of dollars of sunk costs, dozens and dozens of specs, unbelievable complexity that infects all other actually useful specs (like Scoped CSS which cannot proceed properly because effing Shadow DOM), extreme zealotry and complete unwillingness to engage with anyone even mildly critical of web components.
All this results in a strong desire to keep going and promoting this even if no one can even say what the "done" state is for them. Or what is the actual goal, since that goal changes every few months.
However, there are now hundreds of millions of dollars of sunk costs, dozens and dozens of specs, unbelievable complexity that infects all other actually useful specs (like Scoped CSS which cannot proceed properly because effing Shadow DOM), extreme zealotry and complete unwillingness to engage with anyone even mildly critical of web components.
All this results in a strong desire to keep going and promoting this even if no one can even say what the "done" state is for them. Or what is the actual goal, since that goal changes every few months.
[1] https://twitter.com/Rich_Harris/status/1198332398561353728 None of these have any satisfactory solution (for some not even on the horizon)
[2] Even the people pushing this stuff realise how many issues they have: https://w3c.github.io/webcomponents-cg/2022.html See how many of those are not even close to even being discussed