Reserved doesn't mean it always talks about the value of token or money. We're all aware the volatility of the bitcoin which can affect its value from time to time. But it doesn't mean to hold it just to gain profit but to reserved it in a long period of time like a gold where we can see in other banks. In any economic situation having a reserved is a good way to survive such fall of the economic and the market. And also I share to you my experience from my grandma, she always keep old money from the past years some of them is like 30 years old already. But if you ask me how much they worth each? They worth like $200 but back in the day its value only around $1. We choose to reserve it for a long period of time which I could compare to this situation.
I think it has to do with the value because if it isn't then they will use any thing or non-valuable things as a reserved. If you will say it has nothing to do with the volatility, then that's sounds better. Bitcoin is volatile but it can still recover no matter how low it dips and then there are times that it can became stable. If they will only look at this, they will not hesitate to use Bitcoin as a reserve.
In fact, Bitcoin can fit better on this position or as a reserve currency because it was a currency but gold is more like an asset. Your grandmas' story was interesting but I think it's different from what we are talking about here.
What she was doing there is more like a hobby of coin collecting but she was lucky that the value of those coins increases instead of depreciating due to the inflation like what happened with the dollar for example. Well, I guess that's because those coins are rare now or considered to be an antique.