I'm assuming they already are using the package manager. The issue is that there are so many dependencies for a single package, and almost every system update consist of updating a bunch of Haskell packages which just clutters maintenance.
Distribution does it job: it distributes upstream changes. It's like blaming a zip file, because it contains many small files instead of a few big, so it clutters maintenance. If you see this as a problem, then fix upstream. For me, it's important to receive all upstream changes in one update.
