I think volatility of the markets happens because cryptos are decentralized and people have less/more power to control the price. That's why it looks risky than fiats. Anyway, in the long run when there is mass adoption, prices have to go stably up.

The reason has to be like now, when people may invest money into crypto because it's price may rise like bitcoin and then sell it to get fiat. Once it is mass adopted and people all over the world are able to use it directly to buy goods, services, pay for university etc. there won't be any case to sell it or if one sells, other would buy it at higher price because he will be able to use it directly.