At the rate that Apple's own cables fray/fail? Man, I'd be happy if it was only two or three.
Besides, most people have at least several Lightning cables just in general:
1 for their portable charger (sure, you can MagSafe, but it's ridics slow)
1 on their computer/in their computer bag
1 for charging their keyboard/mouse
1 for charging on a nightstand
1 for CarPlay (if they have it in their car)
You honestly don't think people unplug and use the same cable for all those scenarios, right?
That's up to four cables that you're gonna get at best a year or two of use out of before the ends start to fray and splinter.
Even if it's four cables... that's still only $16 for Apple.
And cables can last longer than a few years. I've got Anker cables that I've had since I owned an iPhone 6S. And the cable on my desk is even older than that!
My point was... Apple sells $1,000 phones. So the few dollars of revenue they get per person from cables is tiny by comparison.
Hell... if Apple made a USB-C version of the iPhone... they could charge $50 extra for that!
That extra $50 is the equivalent revenue of twelve MFI cables.