as a kid i had a very particular media diet that caused me to seriously overestimate the likelihood that i would, as an adult, own a house containing a secret passage, but even at the time i had this vague sense that secret passages were too exciting to be that common, that adults were simply too boring to put them in---
and i mentioned this to my mom and she was like "oh, your grandparents' house has a secret passage in it, i'll show you next time we're there" very casually
you see, the second floor of my grandparents' house is basically two garret bedrooms and a large landing (which i believe was previously used as a sewing room, but when i was a kid it mostly contained bookshelves and random furniture). on the stairs side, the dead space between the bedroom wall and the outer wall, under the slope of the roof where there's not enough height to do anything else with it, is done as a random little storage cupboard. with a similar random little storage cupboard off the stairs on that same wall. what i didn't know was that the stairs cupboard and the bedroom cupboard are actually connected, so you could e.g. crawl into the stairs one and emerge from the bedroom one to scare the shit out of your little brother, if you were my mom.
and unfortunately this completely destroyed any intuition i had for the popularity of secret passages because apparently ANY house, no matter how seemingly boring, can have them! you never know!!!