Mainly indeed because there aren't many really good 2D games out there.
Sure, there's a ton of nice japanese VN/RPG maker games and there are some others, but there isn't really a large number of 2D games which come close to SS, once you combine all factors like amount of content, art, animations, characters, story, etc.
And worse, those who do come close or are arguably better in some/most aspects, have (very) slow releases, too.
That's why people stick around, even if it would be better for them to just let go and care for something that's actually worth their time. Those who like DC's streams, etc. at least have a reason to be here...