Why does it need to scale? Does my laptop need to scale when I open a 100 megabyte file? No, it just does it in a few milliseconds then goes back idle. What I m

Why does it need to scale? Does my laptop need to scale when I open a 100 megabyte file? No, it just does it in a few milliseconds then goes back idle. What I mean is, 1500 users sounds like a load you handle with a Raspberry Pi in a forgotten corner. I just don't understand what is happening to overload even the weakest of cloud instances?