In my opinion Gold is more stable than bitcoin so bitcoin can`t be that stable so people can hold it in larger quantities or amounts. You can posses gold with you but you can`t posses bitcoin physically so for me GOLD will the world for next 1000 years.
Gold has a much larger market cap, hence it doesn't react in such a volatile way when new money flows in/out of it. If Bitcoin had the same market cap, its price would also be more stable.
Physical possession isn't such an advantage as you think. First of all, you have to store it somewhere. Most probably in a safe or a bank. That costs money. You can also keep it at your home under your mattress, but who does that? Secondly, it's not divisible. How are you going to pay something worth 1/5 of the gold bullion/coin you have? With bitcoin, that's not a problem. Thirdly, good luck trying to cross a border with it. Want to transport it somewhere else? Enjoy the transportation costs.
With digital money, you don't care about any of that.
Volatility is what makes BTC - BTC.
And its cap is becoming bigger with each cycle that comes by - it's already much harder to move the price of BTC: and it slowly will become harder and harder for institutions too, in my opinion.