Because Bitcoin will never be stable.
There will be a cycle where Bitcoin will experience a dump and pump period of the prices.
However, for as long as time, we have already known that Bitcoin price will be always increasing, multiple times, after 5 years.
When the bullish era comes, the new ATH will be always created. It happens so far. And how is Bitcoin being stable? I think it may not be as interesting as now. Moreover, holder will have expectation that Bitcoin will be always worthier and worthier the future
Predicting the price of bitcoin is never easy because of its high volatility so some days will be bullish while some are bearish. But never to the point of making its price stabilized and stop at its maximum price. Holders will always believe that its price will keep surging and even if price corrections hit it, it will always recover and rise up again. This is what the holders keep them from holding their bitcoin.
And even predicting how far bitcoin price will be remains to be uncertain. No one knows actually. The only thing that is certain is it will still live a couple of decades before it will lost its value and slowly deteriorating.
Stability of price is the common reason why most merchants or shops don't want to include bitcoin as part of their payment methods.
As they are still grasping on how they can tackle this concern, they are just checking other merchants how it can possibly improve or affect their businesses.
And for the reason that no one can give you precise prediction, we all are just depending on the market movement as it comes.