At Table 1, since South's 1H might be only be a 4 card suit, North's 4H bid suggested 6 cards. So South knew there was a 12 card fit - hence it was perfectly 'safe' to bid to the '12' level.
At Table 2, West's 4S was a bit unimaginative. A 4D bid would have been a 'fit' jump. With his extra knowledge of a double fit, East would then have been in a much better position to judge that a 7D save was better than risking 6H making.
At Table 3, assuming that North's double showed hearts, South should certainly bid at least 5H
At Table 4, we finally have a well judged auction.
An extra point: Note that 6H doesn't make on a Spade lead! Certainly at Table 2 knowing his partner had 5 Spades and another suit, more likely clubs, but perhaps diamonds, West should have led a Spade.