The Arch (and some other linux maintainers) have made the decision to package all Haskell libraries as separate OS packages and install those as dependencies when you install, say, pandoc. This model of distribution doesn't really make much sense for distributing Haskell binaries, though.

There's a few reasons for this: 1) since most people don't have many Haskell binaries and the few that people use don't share many libraries, 2) Haskell packages are normally statically linked when building executables.

If linux maintainers would simply build/ship pandoc as a single static executable all these issues disappear.

That's orthogonal to the issue. Even with just one package manager, how packages are created and maintained is a separate task.

So, if the pandoc package has dependencies vendored, dependency hell is avoided regardless of which package manager is used to install it.

If, however, the pandoc package has all dependencies listed as separate packages, dependency hell is created, again regardless of which package manager is used to install it.

So this is a matter of policy, not tooling.