SourceForge still provides a few things that other services do not, like full hosting (not just static pages), mailing lists, public file hosting, forums/discus

SourceForge still provides a few things that other services do not, like full hosting (not just static pages), mailing lists, public file hosting, forums/discussions and a bunch of other more minor stuff like screenshots, news, etc which can be helpful if one doesn't want to setup a full site (so on the same place you have both the option to go with a full site or to ignore it and have the service provide most of the functionality you'd need to provide yourself anyway). In addition, as a user it has reviews, categorization with subcategories (which allow the service to suggest other relevant projects), update notifications, etc. So, strictly speaking, SF provides more to projects and some projects do want that so it makes sense to see new stuff popping up in SF. The main reason SF isn't used much these days is that the site had its reputation badly damaged some years ago while it was owned by some shady company that tried to squeeze everything they could out of it. But last year (i think) it got bought by people who seem to care about the service and doing the right things so far. Of course healing the reputation is a hard thing to do. Personally i self host most of my stuff, but i do know of some projects that take advantage of those extra features (e.g. FreeGLUT uses the mailing lists extensively).