Gold is at from stable. There is plenty of volatility in gold prices. Compared to Bitcoin it may look more stable, but any gold chart of sufficient length will give you enough data to see that gold suffers from volatility in the short run.
At least when compared to Bitcoin, gold is far more stable. One of the reasons is that the market cap of gold is between $5 and $6 trillion, while that of Bitcoin is less than $15 billion. So for a 1% change in the gold price, there must be at least $50 billion worth of market cap change.
You obviously omit a few important things
First, the market cap of both gold and Bitcoin reflects the total amount of these assets, produced or mined, respectively, while the price is determined by the amount traded. We don't know how many bitcoins are traded, while with gold it is only a small part of all gold out there. The rest is either stashed away for centuries, or used in jewelry and electronics as well as other industries. Further, there is a multi-trillion market of gold derivatives (so-called paper gold), which heavily distorts the price determination mechanism. In this manner, the comparison of market caps makes no particular sense
If the Bitcoin exchange rates increase in the future, then it will also become more similar to gold. Most of it will be hoarded, and only a small amount will be actively traded. Also, Bitcoin derivatives will appear in the market, once the popularity reaches a certain threshold.