I think that you are seriously overestimating the volatility of Bitcoin these days and underestimating the volatility of most currencies of the world. The fact is most people in particular poor people are forced to use the currency of their country. They have limited knowledge or possibilities to use anything else. Take a look at these sources.
So you actually believed that the volatility of BTC can be the same as the fiats? I think that is unlikely. Even though both of them are currencies but it is just that the other is unique. BTC has a fixed and has a small amount of supply than the fiats, which is the reason why it is volatility is high. Also, he didn't underestimate the volatility of most currencies in the world but he is only comparing there. In fact, he thinks they are much better in terms of stability.
I think none is forced to use a currency even if that currency is from our own country, but it is just that our local currency is much easier to use and then again they are very stable. Another thing is like you said, people may lack in knowledge to check the other.