I don't know about elsewhere on the planet, but in the USA pre-shredded cheese sold at the grocery store is usually powdered with something to prevent the shredded cheese from re-amalgamating. Consequently, this shredded cheese always takes longer and higher temperatures to melt and reincorporate unless it's rinsed off first. Most Americans aren't aware of this, and so often shredded cheese topping on shit just comes out badly