Actually, glass is a very poor conductor of heat... So, folks tend to turn the oven heat up high---or on a stove top---parts of the dish/pot get hot and others are still cool. So, you get uneven cooking and can get burned areas while other parts are still not yet cooked.
Copper pots are used in candy cooking because sugar is very prone to burning and the copper pans spread the heat out evenly--even if the source is not even.
Aluminum, steel, stainless steel (in order of heat conduction--from better to worst--IIRC), are better at cooking. You will also find pots with SS interiors and aluminum exteriors, etc...
Different materials have different problems too... Cooking with salt, acidic foods, etc. can pit, etch, stain, affect materials differently too. Blacking the outside of an oven pan can make it cook better, etc.
There is a whole science behind cookware--not a silly question at all.
How to stop your mac and cheese from burning?--try different pans, temperatures, covered/uncovered, etc. to get what you like. Or find a good cook book that discusses these things in the library. I am not the best guy to answer this question though…
-Bill