I think forums specifically may have recently suffered loss of traffic due to new Google search algorithm. Any format with user generated content is bad for SEO. Add to that people are more and more preferring social media. But traffic is an ambiguous term. It is easy for people here to think there are fewer members online or posting, but the mebers are usually a small fraction of the actual traffic, generally <20%
Yes it seems obvious that many people do not like the new interface, and some members may have stopped logging in (nobody AFAIK has relinquished membership as mentioned above)
But it may be naive to think that out of thousands of members, the complaints about not liking the new interface is representative. Generally people who don't like something will complain, but those who like it or don't mind will just get on with posting - business as usual for them.
I'm not trying to make excuses, I have plenty of my own complaints and have made them known to the owners in no uncertain terms, but we have to accept it is what it is. We staff are in discussion with VSadmin about what we see as the biggest issue that we may be able to do something about, ie the classifieds. But please be patient about that.