That is made to prevent from abusing the merit system.
Example: One had two alt accounts A and B, and each of them had 10 initial sMerits. He would send between the two account the 10 Merits. A would recieve 10 Merits and 10 sMerits and could send to account B 20 Merits. Account B would recieve 20 Merits and 20 sMerits and would have 30 Merits and 20 sMerits and so on. So, if it wouldn't decrease, he could send between the accounts infinite Merits.
To let the merits grow, several sources are implemented.
So it is an ingeniously constructed system.