The key is money.
I heard that in 2017-2018 was the best years since many people can earn a lot money with minimal effort, they only need to tweet, re-post, translating using google translator, spamming 1-2 liner(s) in this forum etc.
After most bounties turns scam, most people leave the forum, many users shift to signature campaigns and the forum still renting the ads banner.
Theymos decide to stop the ads banner, now starting this year the forum ban mixer promotions which make the traffic going down.
How to make Bitcointalk become popular again? enlarge and expand the incentives.
That solution can work but I have reservations about it, I feel like if the incentive to join is only about money, I'd say that it will also attract people that doesn't have anything to contribute here. Plus, there's nothing that can be done in terms of increasing the incentives because the forum isn't that renowned around the Internet so it's really difficult to justify the money that's pumped on signature campaigns, we're already lucky to still have some signature campaigns here advertising here, it's not a matter of incentives to joining I think, this is just my opinion but I think that what we need is more visibility of the forum to the surface of the Internet, it's not enough that we're at the top search when searching for "Bitcoin Forum", we need to put in some ads on other websites, I think that's what we lack here but I'm not trying to say that's the only solution, maybe there are some and maybe this solution that I'm getting isn't even good with the staff and administrator.