I was listening to 140: A Sign of... Stability? - The Bike Shed today and they mentioned there are few package management tools out there that can show you or direct you to a changelog page.
I think Elm has a great solution for that, which I saw just days ago from Evan Czaplicki - Let's be mainstream! User focused design in Elm - Curry On - YouTube:
elm-package diff elm-lang/core 3.0.0 4.0.0
-- see also elm-lang/elm-package - Updating Dependencies
It's a great feature and can really encourage people to update their dependencies more often. I think one of the reasons for why other tools didn't implement this is most libraries/gems/whatever don't have a Changelog that can be easily parsed. I really wish hex/bundler can also have this feature (which seems to be impossible for bundler).