Dungeons & Dragons.
In the 1990's I held a weekly game that was well attended and we usually played 45 weeks or more a year. Add to that going to gaming cons a few times a year as well. And then I would write D&D games that were played in the biggest gaming cons of the year - GenCon, Origins and others.
Now I have a wonky schedule were the only feasible time to play is Sunday night which is not the best option for lots of people. I was always the DM and my players have all moved away or large families so they can't leave their houses/families for 4 hours.
Pretty much the only time I play D&D these days is at Dragon Con. And there's so much to do that I don't want to spend the whole con playing D&D.