Because you haven't blocked the communities that have the single rule that you have to post something if you visit them. I think there's two of them, and when I sorted by all/new they were about all I saw for a while so I blocked them and life has been better.
The 196 community has a rule saying you have to post something - anything - if you visit them. So folks post something to fulfill that rule, and over time it evolved from "here's my random post because of the rule" or something into just tiling it "rule".
I have had the same experience and question. I don't know why there is so much of it, but have found that blocking any community that is named or references "196" seems to take care of it.
I decided that I was never really going to devote the time to get in on the joke and there was way too much of it anyway.
There really isn't a joke to get, it's just a silly community, so if you weren't enjoying the posts you're not missing out. I hope you can rest easy now, friend.