Why doesn't Data.PVector.map increment the last element from 14 to 15? ghci> adjust succ 2 a -- apply a function to a single element fromList [1,42,14

Why doesn't Data.PVector.map increment the last element from 14 to 15? ghci> adjust succ 2 a -- apply a function to a single element fromList [1,42,14] ghci> Data.PVector.map succ a -- apply a function to all elements fromList [2,43,14]