Firstly rust for an installer UI? Does it need to be especially fast or memory safe? Maybe. Does it have nice bindings for a UI layer? Maybe, or did they create the bindings for flutter (a UI framework designed for object-oriented Dart) by themselves? So why flutter? I guess it can do some pretty animations. Being maintained by Google and designed for Dart, it may just get abandoned in some time, amplified by the fact that noone uses Dart, except for flutter.