Downloads are only as fast as the sources have available or are willing to offer. I mean, how much speed are you willing to offer for uploads? Divide that by the number of upload slots & you get the idea. Some people don't offer high speeds/bandwidth, some people offer lots of bandwidth but too many upload slots so it gets divided too many times & only slowish speeds for each upload slot. But then some people don't offer enough slots for their total capacity for uploading. Thus people get queued, etc.