<x-slider> and <x-datepicker> are sorta unique amongst the components in that they are polyfill components- they do things that some browsers already do, but many don't do yet. They're also some of the most popular UI widgets from jQuery UI. We decided to do them because we thought we could make using them much easier than most existing widgets libraries. Most components are novel functionality not found in HTML5 specifications.
Support is already under way for slider in Firefox, and the rest of the input elements are in development. Why don't you contribute to the project instead of shooting off crass remarks about what "other people", "those people", or "they", need to do.
Because I have no interest in contributing to a terrible software project just because it also happens to be a terribly outdated browser. People are in fact allowed to criticize bad decisions without being obligated to fix other people's code for them.
