one way for bitcoin to have a stable value is to legalize bitcoin into a legitimate currency that can be used as a means of transaction in all countries. and crypto currencies are not used as trading tools such as stocks. so the crypto currency has a fixed value and does not depend on trade market demand.
for now, I think it's very difficult to do it. maybe a regulation will help. but, basically, bitcoin is indeed very difficult to stabilize, there is even a difference of a few dollars a day in the increase or decrease. even more so when demand is overwhelming.
If the Bitcoin is stable, the market cap of the cryptocurrency market is not improving and the market will not develop. And I think all of the investors in the market don't want the stable price because if the market stable, there is no profit.