People with a lot of Merit can earn $50 in BTC a week easily and more in signature campaigns. They have absolutely ZERO motivation to give others Merit because if anything giving others Merit will give them more competition in the signature campaigns.
The purpose of this forum does not revolve alone in earning money through participating in campaign signatures. The forum is bigger than that- which is sharing your knowledge about cryptocurrencies in general. It just so happens that the traffic in this forum makes it as an avenue for businessmen to create advertisements.
While its great to offer people a way to earn bitcoin, basing this so much on the merit system is the stupidest thing Bitcointalk has ever done and it has ruined these forums. I must have seen the exact same ETH-shill post in different words 50 times last week in the Altcoin disussion board. Always by different usernames but probably the same people/same guy running all them in his bot network.
The merit system actually contributed greatly in terms of post-quality of users. Lots of brand new users with relatively low activity are gaining hundreds to thousands of merits in a few months. With the merit system being implemented, it reduced the total number of users who farm accounts by ranking up only through activity.