>>49949068
Coming from someone that used to be far more hardcore about Marisa waifuposting, I think the main draw is that she comes across as a very approachable character thanks to a number of traits (she's one of the most approachable hus, we get a lot of content from her perspective which really helps to flesh out her character, she comes across as kind but not a buzzkill, she has several very admirable qualities but she never comes across as patronizing or better than anyone) all of which make her very appealing to a wide demographic of Touhou fans. She's cool and cute, someone you wish you could be more like but someone you could also see genuinely wanting to hang out with you. Her multi-faceted personality gives fans multiple avenues to explore and latch on to, but ZUN also does a good job of making none of her characteristics feel too discordant or contradictory. You don't really get anything like how Sakuya fans are split between silly Sakuya vs edgy Sakuya either because it's easy to accept all Marisas as being components to the core Marisa identity.
Sorry if that response turned into slight rambling.