Why add immolation to non stackables?

• Spell Stacking: A number of spells were able to be stacked. Shield of Crystal, Death Shield, Immolation, Shield of Ice will now overwrite each other. Shield of Air currently can still be stacked but for R36 it will also no longer stack.

Why is immolation on this list? it’s not a shield. it has no defensive bonus. There’s no game that forces us to drop our defense to keep our offence like this.

 

It's a fire focus, increasing your attunement. The others are also attunement, they just happen to be defensive instead of damage focused.

The way it sounds, these types of abilities are about you focusing on a specific school of magic, increasing your capabilities with that school (and getting some other benefits as you do). It doesn't make sense to have multiple focuses simultaneously.