A gaming niche grows into a major genre from innovation and unique ness along with a strong community adoption. PBBG Games, Pet Games, Sim games are strong prime examples of these, as they've provided unique ness and innovation over the years.
Crafting is also a strong suite of RPG games, which we saw a rise back in the day in the early 2000's, but these features are also now apart of other niches as well.
Most niches also see a rise when they're fun and provide a ton of entertainment to users as well.
However, generally speaking when the community aspect is stronger than the game play elements, a niche can grow a lot stronger than any other niche. The community can make or break a niche.