Missing SCSS stylesheets

[meritoo]

Installation

$ bower install jquery-ui-sass -S
bower jquery-ui-sass#*      not-cached https://github.com/jhilden/jquery-ui-sass-rails.git#*
bower jquery-ui-sass#*         resolve https://github.com/jhilden/jquery-ui-sass-rails.git#*
bower jquery-ui-sass#*        download https://github.com/jhilden/jquery-ui-sass-rails/archive/v5.0.5.tar.gz
bower jquery-ui-sass#*         extract archive.tar.gz
bower jquery-ui-sass#*        resolved https://github.com/jhilden/jquery-ui-sass-rails.git#5.0.5
bower jquery-ui-sass#^5.0.5    install jquery-ui-sass#5.0.5

jquery-ui-sass#5.0.5 bower_components/jquery-ui-sass

Result

$ ls -al bower_components/jquery-ui-sass/app/assets/stylesheets/jquery-ui | grep scss
$

Question
Why there is no *.scss stylesheets while I'm using bower to install? In repo the *.scss stylesheets are available: https://github.com/jhilden/jquery-ui-sass-rails/tree/master/app/assets/stylesheets.