When I was going to college I worked part time at one of the major chains. I made minimum wage, whatever that was 30 years ago.
I didn't expect anything more than that because I had no skills or experience, and none was needed to be a cashier. Frankly, you could train a monkey to do it, and this was before scanners. It doesn't really matter how long you do it, or how old you are. Those jobs are not meant to be careers. If we all agree that a non-skilled, low risk job should be paid $15 - $20/hr, why would anybody become skilled. The trades are dying as it is, and now you want to pay somebody to run a cash register or stock shelves the same $$ as someone who apprentices/trains for 5+ years and invests in tools and equipment and has real skills.
The energy sector isn't an equitable analogy. Yes, you can make pretty good money starting out, but it's physically demanding, dirty work with a fair degree of risk of injury. They pay more because of this, not out of benevolence toward the work force.
The retail and service sectors in general, are low pay, and always have been. They are low skill jobs, that should be filled by low skill workers who are either just entering the workforce or are looking for low demand supplemental earnings. If you have a family to support, learn to do something that pays more, or start your own business. Or become good at sales where you have the opportunity to earn substantially more and are offering something of value to your employer.
CB, I get what you're saying about smaller towns that don't have many employers to choose from. But if someone really needs to make more money, they need to forge their own course and solve their own problem. There are always options, one needs to find them for themselves. Like you have said, the world can be brutal, and it's not someone else's responsibility to make it easier.