Download speed depends on a lot of factors, not just the speed of your connection. It also matters how quickly the server can send the file to you, and the speed of intervening links in its path to you.

Think about it like a big road network. Your computer is like a warehouse with a big loading dock and several lane road coming to it. Even if you can accept and unload 10 trucks an hour, if the supplier can only send 5 trucks an hour that is how much you will get. Different suppliers can send different numbers of trucks but it would max out at however many your road and docks can handle. It might also be the case that road work between you and one of the suppliers slows traffic so only 3 trucks an hour get through, so neither you or the supplier is the real limiting factor.