I think Sourceforge fell from grace because of underhanded tactics like hijacking projects and bundling adware no-one wanted with their downloads, then lying about it.
I never once thought "Sourceforge is boring". I thought they became villains.
To be fair though, they declined in popularity and mindshare and had a change of ownership a few times before it came to that. The sourceforge that served up malware in 2013 bore little resemblance to the one from the 90s.
I feel like it was more like: their offerings were no longer unique, the original team probably moved on, they couldn't make money, and they turned to desperation.
I thought it was because they started bundling adware with software without telling the creators of that software.
Yep [0], after been bought by Dice (they also drained off the Freshmeat and Slashdot communities around that time, then froze the former "as a result of low traffic levels").
I've looked at some tools used by Google - mailing lists, Gerrit, etc - none of those look fun. For a casual like me, fun is important.
I don't do much with open source because I don't have the headspace, willpower or persistence to contribute much so the discussion is a bit wasted on me, but I've used both Github, Gitlab and Stash (Atlassian) for work projects; the feedback loop that tools like this give is super important to me.