Though couldn’t a teenager (older than 14, but still) understand the value that deferring paying for something is useful in context to a part time job? I would only get paid at certain days, and knowing generally what I’ll get at the end of the month after tips and hours, I could budget for that number rather than what I have in the moment.

Then the teenager might ask, sure, that's credit like a bar tab or whatever and credit is convenient for all kinds of reasons, it's just, why do you need a whole other company to get involved and issue a specialized card to do that? Why doesn't the bank just say "we'll let you overdraft up to $4000 without any fuss but you'll have to pay interest on the negative balance"?

Because if you get scammed its easier dealing with a credit card company than your bank

Why? (5 “why”s in total)

Because when your credit card is scammed, its the credit card companies money that has been stolen so they are want to get it back. When its your debit card being scammed, its your money being stolen, and any help to get it back is just a cost center for the bank so they don't really invest in this side of their business like credit card companies do.