People are lazy.
Even when I was in my 20s, I applied for lines of credit as every bank will sign you up. I never bothered using it, but got a few just in case I needed it. I still have them now as accounts in my online bank. Just dormant. They surely send everyone mailers too. LOC rates are much better than CC. The only caveat is that you usually got to pay back more per month (like 3% of a balance) while a CC lets you slide with maybe just paying the minimum 1% of the balance. Doesn't sound like a big gap to me.
Interest rates have shot up like crazy lately so who knows what a LOC is now, but most people is probably like prime +3%. So maybe you pay 10% tops. If this was years back, a LOC would be probably like 5%. Anyone with good standing and assets can get away with prime only which at the time was probably 3%. Why pay 20%? If someone is that desperate, skip the CC and do LOC. It just takes more handling as you get cash and need to dole it out when you buy stuff as opposed to pulling out a card and buying anything on a whim. And if you have LOC accounts, you got to reactivate them periodically to use it as they will go dormant status if you never touch them for like 6 months.