Well, lets have an example if a person posts few posts a week and they are mostly spam posts and then there is another person who post 50+ posts in a week but all of them are good ones, then whom we will think is spam poster?
I think the quantity of posts have nothing to do with the quality of posts. Some persons may have a lot of time to write a lot of constructive posts throughout the week.
You're right, don't get me wrong. However, the more a user is posting, generally means that each post will be of less quality, especially if they're looking to meet a target. However, that's not always the case. I remember quite a few users that were massively active in posting, and one of them is a global moderator now; hilariousandco. While, I don't know how much they were posting at their peak, they were posting quite frequently compared to others, and their quality didn't really dip as a result. So, it can be done.
There's a few examples of this though, even to this present day. I've also gone through periods where I'm much more active, for example the last few years have been absolutely crazy in terms of sucking up my time, and I think it was the back of Covid. Only now, I've starting to get my free time again.