There are many things that could cause it, even normal economic swings. Most of the time there are bull runs that drive the price up and eventually it faces a "price correction".
Price correction down to 30% is also possible after a an unexpected long bull run, crash of a big well known centralized exchange can also trigger such thing to happen too, ETF being disapproved and them being forced to dump all their acquired bitcoin could also lead to that 30% drop, 30% drop is something that’s very easy to happen, and their are many other factors which can trigger that just as you have mentioned above.