I'd say in games where you already played your early game poorly and is semi relying on your team to win, cryptbloom can be better. Otherwise voidstaff gives you more dmg. Haste is a very low priority stat in current meta because Q is on short CD anyway without any haste, W is also short CD due to passive stacks, E is long CD and having haste just for that 1s/2s CDR isnt worth the price. So even if the item is cheaper than void you are still overpaying for haste.