I read that launch pads need to be refurbished after every launch. What stuff on the pad takes damage? What is stopping them from covering the "stuff" in some sort of flame-retardant, explosion-proof material?
Rocket launches are extremely violent. Launch pads are already built from "flame-retardant, explosion-proof" materials like steel, concrete and fire brick, and they're often water-cooled during the launch.
Despite all that, the pad gets damaged over time. Most of this damage is superficial: paint burns off and has to be replaced to prevent corrosion, small items like light fixtures get blown away, concrete spalls and needs surface repairs, the occasional brick is blown away.
You could prevent this, but then you'd need to build the launch pad like a battleship: cover everything in foot-thick steel plates. That would be more expensive than the current solution, and it'd make maintenance more difficult due to reduced access.
A major part of "refurbishing" is just a check: it's a large structure, so this takes some time.