Being able to recycle numbers is the difference between "this can work for a few years at full scale" and "this can work forever". IPv4 can't even reach the first level. It can't even give out one address per human.
I'm sure you've seen the idea that an upgrade to IP could have just added another octet or two and changed nothing else. It would have worked pretty well to prevent us running out of addresses, with 40 or 48 bits.
Well, 16 digit credit card numbers are a hair under 50 bits. And full-size 19 digit credit card numbers are a hair under 60 bits. That's plenty. You can give out a million of them to every person. If we couldn't reuse, they would eventually run out. Because we can, they won't run out.