I don't get how containers address "dependency hell". Is there some language that only supports installing libraries system wide? I've used a lot of different languages and yet to come across one.

I've worked on projects where the original dev has used containers for everything. It's super clunky and annoying. I don't want to use a different bash config just for working on that project. I've set my own up for a reason. All it makes me wonder is what are you afraid of? Why do you feel the need to isolate dev projects to this extent?