It is extremely complicated to do so yourself.

Handling energy efficiency/a11y/i8n is non trivial in any language, using the paved road of the system's native implementation solves for many of those problems out of the box.

You would need to reimplement all of that in D lang for your UI layer, and all you wanted to do was build an application to solve a problem, you weren't in the business of building a UI library to begin with.