Why aren't there existentially quantified type variables in GHC Haskell

Question

There are universally quantified type variables, and there are existentially quantified data types. However, despite that people give pseudocode of the form exists a. Int

Answer 1

It is unnecessary.

By Skolem's Theorem we could convert existential quantifier into universal quantifier with higher rank types:

(∃b. F(b)) -> Int   <===>  ∀b. (F(b) -> Int)

Every existentially quantified type of rank n+1 can be encoded as a universally quantified type of rank n

Answer 2

Existentially quantified types are available in GHC, so the question is predicated on a false assumption.