Why not give Nexus Turret something defensive, like 5% damage reduction from Champions only?

Almost every LCS games I watched, someone from one team has to get caught out & made his team die, and after that the winning team can just safely take their time & kill the Nexus. From there, the Nexus turrets standing high & proud looks nothing more than harmless falling leafs.

So here's my proposition. Why not give the Nexus turrets receiving 5% damage reduction from Champions only? At least this helps differentiate them more than Inhib & Outer turrets.