Timeout in Haskell STM monad

stmtimeout.hs

-- important: compile with -threaded

import Control.Concurrent.STM
import Control.Applicative

-- |Wait for STM action specified amount of time and return value of action or default value if action times out
stmTimeout' :: Int -> a -> STM a -> IO a
stmTimeout' microseconds defVal f
	= registerDelay microseconds
	>>= \timeouted -> atomically $
		f
		<|> defVal <$ (readTVar timeouted >>= check)

-- |Version of stmTimeout' that returns Maybe instead of default value
stmTimeout :: Int -> STM a -> IO (Maybe a)
stmTimeout microseconds f = stmTimeout' microseconds Nothing (Just <$> f)

Why does this require -threaded and is it still the case with modern GHC?

gist was written for 8.something, but i believe -threaded is still required, per hacakge https://hackage.haskell.org/package/base-4.16.1.0/docs/Control-Concurrent.html#g:5