Mate, teams hit the ball into one channel & come at us down the other & through the centre. Our players can't vacate the centre, which leave both undefended wings as areas of attack & danger.
Since we lost our fear factor, teams have been using the same attacking tactic against us time after time. If we had four at the back, the opposition wouldn't have two empty & undefended forward areas of the pitch to attack us from.
If you look at the increasing frequency of similar attacks we face, that's where our main vulnerabilities lie. It's no coincidence.