Let us be realistic. I understand we all want Bitcoin to be a global adoption and from your own explanation, most if not all the traders you mention don't do big numbers in terms of cash daily, or even if they do, it is usually in bits and that is where the problem is. Why were people complaining so much when ETH fee was high? even then you would remember that the whales cared less about fees that's the same problem that these petty traders will encounter with their daily trades with Bitcoin. They do little transactions at a time mostly amounting to small satoshis and if they will be paying fees for every transaction plus price volatility, you can see why people on that level of education as you mentioned might not adopt it for transactions.
Transaction fees and price volatility are some of the things that shop owners may worry about. LN can certainly help them handle small transactions, but it's hard to expect them to be willing to adopt bitcoin as a means of payment especially since there aren't many automated options for converting bitcoin to fiat yet.
For some countries, crypto taxes are starting to be set and enforced by the government. This will charge each bitcoin owner to pay more fees when they convert their bitcoin to fiat. Obviously in my opinion this is another obstacle if shop owners are going to have a lot of considerations before adopting bitcoin as a means of payment.