Purpose of Network.Wai.ResponseReceived

Specifically, the documentation states “This is to avoid the need for Rank2Types in the definition of Application.” I do vaguely remember why the Application type cannot be simply Request -> IO Response, the explanation being in a talk about wai, but first thing that comes to my mind is changing the type into this: type Application = forall r. Request -> (Response -> IO r) -> IO r Without enabling any extensions, this works on GHC 9.10.3. But seemingly using NoRankNTypes makes it not work, so...