Retailers accept fiat because it's easiest in every way. There needs to be a benefit for the retailer for them to start accepting it, then the public will need to see one or many benefits to using crypto over using their cash/debit/credit. We're a LONG way away.
Retailers won't use cryptos as long as we have this volatility like we have it today. Because every retailer has to pay his rent, insurances, employees, electricity, gas, food ... with fiat. If you want to sell something with the chance, that the amount of currency you got will halve its value tomorrow - will you sell it? You won't. Only if you could change the currency you got immediately to fiat. So cryptos will be only a vehicle for fiat, until it becomes stable. Do I see a chance to make cryptos stable? Only with regulation. But the idea of cryptos excludes regulation. Difficult situation, which is in need to become cleared. Until then: Some cases of use are demanding a specialized cryptocurrency. This cases keep the affiliated currency alive. The more usefull the case is, the better for the related coin. But usefull things come and go. And we should always remember: The whole cryptoworld is deeply addicted to technic. Let the internet crash, let the quantum computer rise - the cryptoworld you know today will be unrecognizable tomorrow...