Earlier quoted context omitted.
The "problem" with native controls is that they might visually clash with the design of your website. That's why everybody implements their own controls or uses libraries like jQuery. And sadly, that's probably why we don't have good default controls.
> The "problem" with native controls is that they might visually clash with the design of your website. CSS can fix that once good native controls are implemented.
Another issue is styling checkboxes to use custom images for the different states (including hover and pressed styling).
The CSS UI spec (https://www.w3.org/TR/css-ui-4) doesn't detail any of that, and the WHATWG HTML spec only defines the values of input fields (e.g. https://html.spec.whatwg.org/#the-input-element), not what parts of things like a date control are available and how to style them.