Haskell packages in arch are dynamically, rather than statically, linked, which pulls in a large amount of transitive dependencies (reportedly in the neighborhood of a gigabyte). The maintainer has a pretty reasonable (to my eyes) explanation[1] as to why this is the case, but admittedly if I were an arch user I'd probably find it a bit annoying.
[1] https://www.reddit.com/r/linux/comments/9emwtu/comment/e5qss...