[bryanlarsen]

Rust is often the best language for the meat of your program; it's nice to use it for the gravy too.

Many, if not most, programs are not primarily UI's. They exist to control something, calculate something, transform something, et cetera.

All of these need a human interface. Perhaps a command line and a config file is sufficient, but often an interactive UI helps.

You could create an API to your rust program and then write the UI in something else, but there are huge benefits in writing both in the same language.