They do not miss it all, it's exactly what's killing them. Take Pep's City out of the equation and history would have been very different for Klopp's Liverpool. Without City these would have been glory days for Liverpool, they are fully aware of it. I mean they did achieve more than decent stuff (and credit to them, as you say), but instead of marking a glorious era in their history books, Klopp's Liverpool will mostly be remembered for constantly finishing second best, behind one of the greatest (if not the greatest, according to Lopetegui) teams in the history of the sport...
So it's not really difficult to understand their attitude, is it? A depressing realisation combined with that culture of theirs destroying their souls, leading to unreal levels of poison and hatred. Hating City has become a way of life for a large part of their fan base. Fact. Nobody should be surprised, if you ask me...