Correlation doesn't equal causation. The reason the Alexa rank was so high in early 2018 was due to the preceding bull run. Everything was in the green. You could buy any useless scam token and still make a profit from it. The forum was overrun with bounty hunters, spammers, and scammers. There were new altcoins being launched every hour, and new bounty campaigns to go along with them. Thousands of accounts were created just to spam utter trash for the signature rewards. The death of 99.9% of these altcoins are what reduced the traffic to the forum, not the merit system.
Also, it is clear that most threads from the newbies are not given much attention because of how they structured their article.
Most threads from newbies aren't given much attention because they are either outright spam, have been discussed 100 times before, or they've just copy and pasted from other places (or even worse, tried to hide the fact they are copying and pasting by "summarizing" content they don't understand and introducing multiple errors).
If you noticed well, you will see that the signature campaigns are getting closed because companies don't get exactly the kind of traffic they used to see.
Good. The vast majority of signature campaigns just encourage spammers.
Your problem is that you view the forum's primary function as enabling people to earn via their signatures, and the merit system as a hurdle en route to that goal. You're wrong. The primary function of the forum is to encourage meaningful discussion, and the merit system supports that goal.