In reality, building anything complex is a huge pain using web components, particularly because it is hard to author them with appropriate level of styling API and accessibility support. In my experience, web components are fantastic for consumers but terrible for the authors.

Still, the advantages are clear: they don’t need any special runtime and can be used with other JS frameworks.

Another thing in favor of web components is support for custom registries which make gradual migration from one version to another trivial. AFAIK, no JS framework has an equivalent of custom registries.