Consider how excruciating it is to try and view source code on SourceForge compared with GitHub. On the latter you are literally shown a listing of files with the README already open for any given repository.
Sourceforge has this absolutely useless "Download" link where you have to grab an archive, extract it, dump it into your text editor, and only then will you find out it's not what you want.
It is not an understatement to suggest that Sourceforge is by people with no idea about open source.
This comment is quite simply out of line. SourceForge played a crucial role in the promotion and distribution of Open Source software well over a decade ago. It was the first successful repository that freed projects from the uncertainty of university or personal web hosting, it provided collaborative development tools and multi-developer project management years ahead of Github's very existence, and continues to distribute some of the biggest names in Open Source.
Learn your history! (Man, I feel old saying that)
Freshmeat was never a spectacular platform, but it was the de-facto open-source distribution center at the time. It played an important role in that environment, but was more of a distribution channel than a collaboration tool.
Today SourceForge is the GeoCities of source hosting. It has almost no redeeming features.
It's not my intention to try to one up others with my four-digit UID. All I'm saying is, I was there, I was heavily involved in Open Source at the time, and SourceForge was critical.
Edit to add: Geocities was pretty important to the development of the web, too. Part of me prefers the days when everyone made their own eye-gouging web site instead of relying on Facebook. There was a much more eclectic selection of content available back then.
This is probably largely related to the behavior of their users, though: Github's interface is not a lot more informative than Sourceforge's if no one writes a useful readme, and there have frequently been well-written projects hosted on Sourceforge that have lots of good information on how it works, or how to use it. However, I rarely seem to hear about new projects at Sourceforge, and frequently do see stuff at Github that has well-written introductory documentation accompanying the sources.
I frequently want to read about projects that solve interesting problems, but might not have the interest in installing or using it. Moreover, many people seem to now be using Github as a "Host my interesting document easily" host, which reinforces the "I go to Github to read code / read about code" perception. I'm sure a large part of it is confirmation bias, since most of the interesting code-related things I read about here are hosted at Github. ;)
I don't think it's that hard to see that this is still preferable for many projects.