Why not remake Frozen Heart as the anti-physical damage spell item?

Clearly Omen is the anti-auto attacker item since it lowers IAS and blunts crits.

So why not remake Frozen Heart as an anti-physical damage spell item?

Make it absorb a percentage of the physical damage you and your team take in an aura around you to keep the support-y feel it already has. Because it doesn't make a great deal of sense to have two items that are basically doing exactly the same thing. That might even allow Omen to get its attack speed slow improved since there aren't two items doing the same thing now.