When you have to make 60 posts a week to make $20, people tend to shitpost all over the place.
Any Legendary member (which OP referred to specifically) can make way more than $20/week, and I don't see them as being the problem with shitposts--maybe the drama threads, but members who've been around a few years tend to make interesting posts, if not always substantial ones. It's usually the people who come here for the sole purpose of earning money through bounties that are the problem.
I was just exaggerating numbers for the purpose of making a point.
But i do agree, sig campaigns and shitposting goes hand in hand. Maybe not in the early 2012 so much, but definately around 2015-2016.