I agree with the OP's observation and have been wondering about it. I think part of it is that, over the years, everything has been said about almost everything. For example, I followed the Covid thread closely to start with but now I hardly look at it. I have now identified those who have opinions I respect and I will have a quick look at what they say. If that looks interesting, I might then look at the surrounding posts. I think that there used to be a lot more posters who offered informed opinions or were able to catch one's attention with amusing comments or anecdotes. Basically, there are fewer real characters left to amuse or inform us.