snoyberg/conduit — comment on commit 1ec4176d4fdf5de320c48798e6e7599fb08af247
File: conduit/Control/Monad/Trans/Resource.hs line 250
By snoyberg:

Honestly? I don't know. It might have to do with difference in fixity of operators versus do-notation. I just noticed in my benchmarks that ResourceT was too slow, so I copied the implementation of >>= from ReaderT.