The answer is actually quite simple, the only reason, GitHub doesn't offer a place to upload packages (just a master package) and then provide statistics on those files. SourceForge does provide that feature and even breaks it down on a daily, weekly, monthly, annually, and all time statistics. Of course, too complex, heavy and get many workload on client side on browsers, but provide it and with a lot of space!!!.
A poor but easy reson, guindoser like of course: easy to use and lightweith interface, not much usefully but great for little projects.
For mayor projects that need heavywheith features with stitcs and great control: SF,
For little and short time things, Github for novices.