Why no strict until'?

StrictUntil.hs

import Prelude hiding (until)
import Test.Tasty.Bench

{-# NOINLINE until #-}
until                   :: (a -> Bool) -> (a -> a) -> a -> a
until p f = go
  where
    go x | p x          = x
         | otherwise    = go (f x)

{-# NOINLINE until' #-}
until'                   :: (a -> Bool) -> (a -> a) -> a -> a
until' p f = go
  where
    go !x | p x          = x
          | otherwise    = go (f x)

main = defaultMain
  [ bench "until" (nf (until (> 1000) (+ 1)) (0 :: Int))
  , bench "until'" (nf (until' (> 1000) (+ 1)) (0 :: Int))
  ]

-- Results:
--
-- until:  OK
--   11.0 μs ± 698 ns,  47 KB allocated,   2 B  copied, 6.0 MB peak memory
-- until': OK
--   5.68 μs ± 297 ns,  16 KB allocated,   0 B  copied, 6.0 MB peak memory