If there's one thing I've learned from 25 years of reading political message boards, it's that many posters who don't post nonetheless continue to read the boards on a regular basis, even while their anger and bile builds up against those who are posting. And in most cases the absent posters who still read the boards are conservatives who are no longer willing to post because they can no longer effectively defend the policies and actions of Republican leaders against the board liberals. So instead, as you said they just lurk, and fume and occasionally do post to lash out at board liberals. When the old IC ZZLP was deactivated it was something over its last couple of weeks reading all of the Trumper posters who flooded the board - many of whom had either never posted but read the board regularly, or Trumpers who had not posted in years but still lurked - to vent and rant and rave about how glad they were that the board was being shut down because it was dominated by liberals and was so unfair to them and they just hated the board even though they couldn't keep themselves from reading it all the time. The resentment of so many Trumpers is very real.