I thought Compendium was wonderful. Not the biggest space, but it had separate sections for literature, sf, feminism, politics, psychology, spirituality with a really knowledgeable person running each section, plus those massive tomes that enabled you to look up/ trace and then order difficult-to-find books (pre-internet days). From what I heard (not necessarily correct) the cooperative/ managers just decided they'd had enough and wanted to retire. I know that leases in the area were being renewed for ridiculous prices, so that might also have been an issue. Likewise the internet was just beginning to hit its stride. However I think they just decided the time was right rather than being forced out of business by financial circumstances. Camden had become such a popular place for people to visit that they would always have had plenty of footfall. They'd been going for a while, back to the early days when they used to have to hide comix etc under the carpets in case of police raids.
When it closed I missed it greatly: it gave a whole purpose to visiting London for the day.
I knew "Dark they were and Golden Eyed" less well. I think I made the pilgrimage just a few times when visiting London. I moved to live in London in 1982 and it might already have closed by then.