Case in point, clear. Or "typed nils". Or accidentally swallowing errors because you had to handle them manually. Or reimplementing higher-level job control on top of channels every single time.
Can you please explain this?
But as an example, if you wanted to have any sort of higher-level management of goroutines (for example, a bounded number of background workers) you get to rewrite or copy-paste that code every place you want to accomplish that. A library couldn't exist to abstract away the idea of a pool of background workers because it can't know in advance what types you want to send over your channels.
Again, I wouldn't be surprised if post-generics there's a library now to do this for you. But for years if you wanted anything higher level than raw channels, you're basically on your own.
I don't think the implementation details matter to a user of a map or a slice (or an array for that matter) - they're language builtins (as opposed to span, vector and map in c++ which are library types).