Why does everyone put CD runes on Brand?

The man is on fire for gods sake. If anyone needs to cooldown, it's him.

...I will NOT apologize.

Were you looking at mid brand guides or support? I could see supp making use of CDR

Because you're supposed to walk into lane with the confidence that you can hit your skills and dodge the enemy's.

The most important part of most midlane mages is being able to apply CC and output DPS.

That's what CDR/lvl is there for. Most slows, stuns, and rotations.

Also, these when making these guides, they do it based on whether or not you should be hitting these skills.

For example, nobody banks on ever hitting Ekko's W, but with Brand you should be able to land skillshots semi-regularly.