problems with trace

After I load the following into ghci and call main I expect to see "norm"
in the output 3 times as I have called it 3 times but it only shows once.
Why?

traceBug.hs
---------------
{-# OPTIONS_GHC -Wall #-}

import Debug.Trace (trace)

norm :: [Int] -> [Int]
norm  = trace ("norm") id

main :: IO ()
main =
  do
    print $ norm [2]
    print $ norm [2]
    print $ norm [3]
---------------------

ghci session

% ghci traceBug.hs
Loaded package environment from
/Users/gcolpitts/.ghc/x86_64-darwin-9.8.2/environments/default
GHCi, version 9.8.2: https://www.haskell.org/ghc/  :? for help
[1 of 2] Compiling Main             ( traceBug.hs, interpreted )
Ok, one module loaded.
ghci> main
norm
[2]
[2]
[3]
ghci>

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