GitHub isn't a commodity that excels only because of it happening to be popular. People choose GitHub because it's both popular and good. It has competition, some of which are better for specific circumstances, but as a whole they don't execute as well.
Let me contrast with Facebook – it was only good, in my opinion, for a brief period starting in 2005 which happened to coincide with my freshman year of university. As it grew and changed, I found myself and very many of my peers hating each significant change. The only reason I've kept an account is because it's popular – it stores some weak social connections which would be otherwise lost.
I've never used gitlab, but I find bitbucket to be identical to github in every way that matters.
(Most of out repos are public but some things you want to keep private at first.)
It's way above being a simple repository storage which isn't a trivial think to setup to begin with just watch the various talks from BitBucket's core team.
As long as everyone else has to play catch up they will be fine. And i don't see sourceforge as being comparable unless you just look at a project hosting in it's most basic form in which Google Drive or Dropbox can also fit in that category.
Sourceforge offered shell access for SVN; Google drive and dropbox wouldn't support branching, merging etc. To say sourceforge is in a category closer to them than to github is ridiculous.
It's worth noting that 10 years ago, this same statement was true of Sourceforge.