The Wall draws power from the King, what if the Glaive did too? So here's Noctis who hates thinking about anything to do with his title, ruling, or anything else that will remind him that his father is slowly killing himself. Noctis, who figures out that the Glaive, while not as bad as the Wall, are still draining his father. So he fixes it.

He finds a Glaive that actually likes/respects/loves his father *coughNyxcough* and tells him exactly what the magic he wields costs; then he offers to fix it. He's the Crown Prince, his father is not the only one connected to the Crystal.

So Noctis eventually has most of the loyal Glaive tied to himself and Regis notices that the drain has gotten less.

+Maybe Regis survives because of that?