Cashing out will be less and less a problem, when economy will become more and more tokenized and fiat will lose its importance when everyone will realize it is toilet paper baked on false debt.
I think that there is nothing to understand, because it is feat that is a more desirable and easy way for people to pay for goods and services. The fact that many people do not have any money is a completely different matter, but the ease of using Fiat speaks specifically for their preferences.It is not because you don't understand that there is nothing to understand.
Cryptocurrency are likely to totally change the economic system, which is not sane today. But I don't speak in very short term of course (that is why I used the word "will"). I simply say that at some point, the problem of cashing out will disappear, because it will be very easy to buy things with it like with fiat today. Big companies will mint their own token, and the states will continue to lose the influence they have already began to, and with it, the fiat currencies, which have no more value than the power of the states to impose it to the populations.
Moreover, concerning cryptocurrencies, the first rule is to buy only what you are ok to lose, so you don't need this money, and it would be too bad to cash it out, to spend it in a snack or in a pair of shoes. Remember the 10000 btc pizza.
Cryptocurrencies are a long time bet.
have a nice day 
