I initially fell in love with a fantastic remix that popped out on a youtube video recommandation and planned to find where it came from and nothing more, but the sheer amount of everything I keep running into during my search got me more and more intrigued and passionate about this series. I'd also say walfas videos and the legendary meme videos à la Alice stole the precious thing, McRolled, and Cirno's perfect math class also played a large part in me discovering the characters and the memes.
I'd say the culture, the community, the various works (music, book games, both official and fanmade) hooked me on one side, and the discovery of the universe, characters and much later even the games got me wanting to see how far the rabbit hole went. We're really, REALLY low production here, but still the series manages to be more immersive than a lot of AAA games with big boi budget production with experienced writers and realistic graphism + physics
The almost-all-female-cast-series niche wasn't quite as abundant as it is nowadays in the past, but that part is still one of what made Touhou kinda unique back in its golden era. It's not such a unique point nowadays as there are for example plenty of popular gacha franchises that are OVERLOADED with waifus and boobs and sexy voice acting and high production value and actual marketing and lots of content (all of which we pretty much don't have much of), but decades of community history and fanworks just CANNOT be replaced by any random new-hot-thing, and honestly, none has managed to charm me quite the way Touhou did.
It's way past its golden era, but we've entered a time where there are more people who are somewhat aware of Touhou and even a much easier access point through Steam (revolutionnary) or the various mobile games which are millions times more appealling to casual audiences compared to the bullet hell games.
