while it sometimes may encourage shitposting, it also rewards long term participation.
Shitposting has its own reward.
Long term participation is usually something that happens because people have things to say. I believe that encouraging the idea of "posting more" regardless of the content can only lead in a degradation of the average content quality, because:
- Users might force themselves to make threads/answer posts even though they have nothing useful to add (more bad posts),
- Users who are writing an answer, and then see that they aren't going anywhere with it, might feel compelled to post an incomplete, nonsensical, wrong, or irrelevant answer anyway (lower average quality of posts),
- Most of all, rewarding high post counts is definitely something that affects immature people more, and they are the people most susceptible to be affected by the first two points).
As to your last point: I'm pretty sure avoiding shitposts altogether is a better outcome than deleting and punishing a huge number of shitposts. "Prevention is better than cure", yadda yadda... Bad posts
could be seen by other people (including guests) before they are moderated away (which is unsightly, no matter how fun we think some of them may be), mods
could miss some of them, they
could (and actually do) lead to more bad posts and backseat moderating (mostly from the immature people who want to increase their post count and think making posts like those is okay), it gives more work to the mods (whether they mind or not, it's still additional work)...
All those effects are arguably not very important and could be ignored, but so would be the benefits. This system seems to be, at the very best, useless.