The things that make it through these periods are the stuff that is seen as useful to the folks in between. This is why we get a lot of religion, the odd bits of sciences stuff, a lot on growing food and snips of history if lucky. Heck for the might of the Roman empire, we only have 25 seconds of sheet music remaining. It is also funny how little we know about some of the Emperors. Things like, they had children, we do not know their names or if they survived childhood. The gaps are huge.
The things that survive are the things other think are worth surviving. Hygiene practices yes! Tiktok... no.