ONLY Malphite Jungle can Carry this... How to Play Malphite Jungle for Beginners (Best Build/Runes) 

Because 1. 400 gold is a lot. 2. The attack speed slow would be helpful against the more of the enemy team (diana and graves/draven) and helpful for his team and not just help himself to survive longer. 3. As he says in the video he doesnt regard hp as that useful of a tank stat as compared to resistances generally and the resistances also synergizes more on malphite because of his w than they would on other champs (he gets extra tanky and does some more damage when he gets armor)

Frozen heart also gives haste =more damage and utility as you can use abilities more often. Usually I prefer randuins on most champs if the enemy has 2+ crit champs but I think frozen heart works better on malphite for this game.