It's a calculation on the total amount of activity, isn't it? Well, it has been decreased because a huge amount of Jr member demoted into newbies and they couldn't wear signature. Because of that, there is no meaning of continue posting as they will get no bounty.
However, after the new implementation, the activity in meta, was increased decently. So, the same will happen. 10 merits requirement will reduce spamming in Altcoin discussion (No one care that, IMO) while it will increase spamming in meta significantly.