Singpolyma

Sanboxed programming environments are a workaround for the problem systems like cabal have where you don't have a consistent set of package versions that work together, you have all versions of all packages avaialble and then issues can happen (causing people to say words like "cabal hell").

If you use a consistent set of packages for all development (such as OS-provided libraries) this is not an issue.

I work on many (many) projects at a time. Sandboxes (in haskell, python, ruby, C, all my languages) would just add more pain to my workflow.