When I launched
https://bpip.org, there were over 300,000 active members. Now there are 57,000. That prob has a lot to do with it.
But what is the cause of this ? The forum owners should be interested in identifying the possible causes and taking remedial measures. Like suppose, the search engine rankings are affected, there should be SEO done to attract more new active members on the forum from time to time.
Bitcoin and Cryptocurrency were gaining a lot of boasts, that was when many great projects were coming in, so many free coins from airdrops and you only needed to join Bitcointalk and post your usernames.
The forum is still doing great we have a saying that the wine tastes better as it ages, forum still gets massive traffic because they are on top of the many keywords related to Bitcoin-related.
Some keywords can be found here in Bitcointalk, I don't think Bitcointalk will lose its authority and they get more as time goes on.