Two distinct things are getting mixed together here. The heat shields in the game now are "abalative," which means they work by shedding material. The material gets hot, then is eroded away by the gas flow, taking the heat with it. Relatively inexpensive materials can be used for this (relatively!), and they can only be used once. By contrast, the shuttle's shield was made out of unusual materials which would absorb and re-radiate a great deal of heat without suffering damage, but with the added problem that they would break or come loose occasionally, requiring maintenance between every flight. So they were re-useable in concept, but still couldn't go straight from one re-entry to another. In short, re-useable shields are a very different thing, and would need to be handled differently in the game.