Long story short: They solve a problem that is attractive to solve in a way that is not super useful for how most people want to develop an application. They're client side only (in practice) and poorly compatible. The developer problem they set out to solve is mostly solved elsewhere, better, by other frameworks. What those frameworks don't solve is usually not the parts that are useful about Web Components.

Which is a shame - as there are some genuinely good ideas in the set of tech that makes up Web Components. They just aren't very attractive to work with.

I kind of feel they need to scrap it and come up with a compelling v2 that uses what we know now.