I remember participating in one of these forum where they offered to pay user in ETH after reaching a certain amount of post, which turn into spam fest quickly. On the other hand, I've seen so many forum dies because they can't attract enough users simply because they're too identical with existing popular forum like BTT which allows them to earn while posting. I guess activity and posting incentive are quite important for forum longevity. Making everything too centralized can also turn off some members from participating in forum discussion and so on.
Some forums also reward users with BTC or ETH for their activity, but this has been abused and spammers have taken over forums when the quality of posts is not checked or evaluated. I think bounties are necessary for forums, and bounty managers will be the ones to ensure that only deserving members receive rewards. Up until now, no automatic mechanism can do this job in place of humans. AI is a possibility, but I doubt its effectiveness.
I think AltcoinsTalks has found a way to continue existing in the crypto market: maintaining a friendly community, having its own token, and supporting bounty campaigns from crypto Mixers and new projects. Listening to and applying smart and insightful suggestions from the community is also a driving force that helps AltcoinsTalks become better, have more valuable threads, and reach more crypto members and investors.