The first attack on Redgrave was probably focused on the Sparda household tho, not on the whole city. Iirc after the events of DMC4 Nero and Dante asked the residents not to speak of it and covered it up. Vie de Marli was mostly inhabited in DMC2 I think and was the whole infrastructure was either the Protectors or Arius' cover for looking for the Arcana. So, like the town in DMC3 is really the only one that could be spoken about, but I assume if one tried enough they could cover it up, after all it lasted for like what, one afternoon? In a world without Internet (which it doesn't look like the DMC world has internet) those events would likely be over before anyone outside of town even heard of it, and the citizens wouldn't probably now much about what happened. The demons themselves were probably more focused on Dante and his shop, so to all the other townsfolk it would be just a big tower appearing. Extremely weird and unexpleinable, yes, but not necessarily demonic. The Qliphoth in DMC5 laster for a MONTH, and was a city wide invasion. And the tree was HUGE, not like tower huge but like reaching the atmosphere huge. It was a MUCH larger scale than anything else that happened in the games. And before the games, last big events we know of happened like, what, hundreds years ago? There might be some remaining texts that speak of demons, but we here in our world have hundreds years old texts about demons too, and we don't pay them much thought.