This is indeed a very vital question you've raised here. As crypto ethusiast, we think that the adoption of crypto currency is more than 70% confirmed, but we fail to release that we are been deceived by the cycle we are in. Now back to the question.
But for teachers, nurses and pensioners, for the grocery store at the corner, the shoes shop, the restaurant, the car repair shop... for these people and businesses what are cryptocurrencies good for? What could cryptos be good for?
Most crypto ethusiast believes that you must know how a particular
crypto work and every protocol that guides it, before making purchases or whatsoever. If this ideology is to be followed, then certain people like the nurses, teachers and pensioners won't find it neccesary.
Have you ever wonder why this people use our traditional banks and credit cards ?, Because they don't need to understand the protocol behind it.
So, if the above mentioned people don't see the need in learning the protocols that guides all these cryptocurrencies, then they can simply use it as a medium of transaction. Investment shouldn't be compulsory, but let it serve as a medium of transaction just like their credit cards and money in banks. This should also apply for those who are not educated.
In conclusion, the less complex it is, the quicker the adoption.