The reason, I guess, is that if it were not so, the King could position itself next to the centre square and never be captured, even if it couldn't escape that way as the requirement is to place pieces on all 4 sides.
(peida) Oma profiili muutmisel kasuta Notepad´i, nägemaks, milline näeb välja Sinu profiil koos html-tagidega (ainult tasulised liikmed). (rednaz23) (näita kõiki vihjeid)