Midfield and forwards are nothing if you have some superkeeper, against those team with much better midfield and forwards can't even produce chances, which is absurd. I would admit that superkeeper can save all 20+ shots, but you earn maybe some 2-3 moments against them. Vincent probably didn't imagine, that such monsters are possible and would have such impact. He expected keepers to wither similarly with fieldplayers, just some years later, but something in formula worked differently.
Meanwhile opportunity to grow up former average keeper to supergeront gives more chances to more teams as otherwise few teams with rare high ST keepers would dominate for decades because here is no financial control and several top clubs in game are in billions of debts. Keepers tend to be also greediest players in game.