Why does folding arrays differ from folding lists?

folding.elm

import Html exposing (text)
import Array as A
import List as L

main =
  let
    a = A.length <| flattenA arrays
    b = L.length <| flattenL lists
  in
    text <| toString (a == b)
  
arrays = A.repeat 3 1 |> A.repeat 3
lists = L.repeat 3 1 |> L.repeat 3

flattenA plane = plane |> A.foldr A.append (A.fromList [])
flattenL plane = plane |> L.foldr L.append []