>>1892166People love Touhou Project for different things. Some like the interesting lore and the colorful characters. Some like the great music. Some are fans of shooting games in general and/or appreciate the bullet patterns.
The main draw of Touhou is that its creator allows and even encourages fans to make their own derivative work based on it. Music, games, anime, manga, porn... you name it.
Touhou wouldn't be as popular as it is now if it hadn't been for the plethora of fanworks based on it.
Now that you've said it, Touhou is quite opposite to the bronies' situation: the games are marketed mostly to the average comiket-going otaku crowd, but draws in young schoolboys/girls too nowadays.
