I guess it really just depends. I've noticed that a lot of popular artists have fanart or tutorials in their galleries, but I don't believe those are the only reasons for their popularity. Having a distinct style also seems pretty important (for example, it's really easy to tell if an artwork was made by Sakimichan since her style is quite distinctive). But there are also certain styles where quite a few different artists seem to have nearly identical art styles, but still get popular since that art style is well-liked by a lot of people.

Original artists seem to have more difficulty getting popular, but the ones that are popular are generally great at being active in the community and getting their name out there, either through quality journals, forum posts, or submitting their art to lots of groups.