Because of the Rabbit.
I found touhou because of a friend, kinda got involved and wondered what the hell touhou is. So he passed EoSD to my computer and I was completely amazed at how hard it is yet satisfying. So, I coerced asked him to pass all his touhou files which starts at th 6 to 15.5. I downloaded 1-5 later on because I was utterly curious.
Pretty sure some people got to touhou thanks to it's oh so wide doujinshis. And so beautiful fanarts.