.su isn't listed because it's still active.
Come 2091, people will celebrate the 100th anniversary of the fall of the Soviet Union, and .su will still be alive and kicking.
But I'm sure somebody somewhere is going to be celebrating.
America's hawkish (neo)conservatives continue to celebrate the fall of the Soviet Union. "Presidents Reagan and Bush Sr beat the USSR!" (Maybe that is an oversimplification of the truth, but it sounds good to their ears.) In 2091, there is likely to exist some intellectual successor/descendant to that school of thought, eager to mark that centenary.
What do the Russian Orthodox think? They went from an authoritarian regime which officially opposed the Russian Orthodox Church to a (still rather authoritarian, but arguably somewhat less so) regime which wants to be publicly seen currying favour with it. I'm sure some of them view that as an improvement. If that's what some of them think, why wouldn't they celebrate in 2091?
What about the countries which gained their independence through the downfall of the Soviet Union? I think many people in many of those countries will be celebrating the centenary of their independence.
For sure. https://imgur.com/gallery/L9VNpP4
heh
There are probably a lot of firms that serve many of these countries, and having a single unified presence at foo.su is probably more efficient than registering foo.ru, foo.ua, foo.kz, foo.lv, etc.
1. Sites that were created back then and just stayed (a very low number).
2. Sites of organisations operating in most of the ex-USSR or CIS countries.
3. People who are nostalgic or associate themselves more with the Soviet Union than with any of the states that exist in its territory today.
4. Just-for-fun types of people.