Price going down = bad news + panic selling + whales cashing out
But what factors keep Bitcoin price stable?
Well, if there is a balance of sellers and buyers.
I think that healthy economic activity and a low level of speculation is what makes bitcoin prices stable. For example if a merchant can start accepting bitcoin as it is right now instead of using a Bitpay API and converting that bitcoin instantly into USD as soon as he receive it, then bitcoin is definitely going to be more stable. We have users doing that but we need big corporates doing that as well.