I can only assume Americans are using so much oil on pizza that all structural integrity is compromised and its more like greasy tomato soup served on flatbread
Too much sauce could be the culprit as well, if the cheese is floating on a lake of sauce while melting you've got problems and another is LET YOUR PIZZA SET FOR LIKE 5 MINUTES. If they're eating without waiting the cheese doesn't have a chance to resttle and will be hard to get a solid bite on so you end out dragging the mass. Also likely is they're using wayyyy Too much cheese and thst mozzarella is turning into a big disc of borderline boccini.
Resist the temptation. Just like, go into s different room for a bit. This applies to most hot foods as well. Things keep processing after they're taken off a heat source and waiting until it's all the way finished does make a big difference.
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