While I agree NPM bloat is a problem, this doesn't seem like too unreasonable an approach to publishing a la cart libs like these. I haven't looked closely at the repo itself, but code generation through build/release scripts is commonly used to manage the issues you describe.
EDIT: Unless I read the source code wrongly, it seems like they actually used the umbrella repo to collect docs and links to all the other components which is the opposite of what I thought was going on here.
EDIT: Unless I read the source code wrongly, it seems like they actually used the umbrella repo to collect docs and links to all the other components which is the opposite of what I thought was going on here.