As I recall, people have figured that at the speed which IPv4 addresses were given out (before they ran out), even if all possible unused addresses were reclaim

As I recall, people have figured that at the speed which IPv4 addresses were given out (before they ran out), even if all possible unused addresses were reclaimed (which would be a huge pain to do), it would last at most, IIRC, a few months more. So it would help some, but would not really be worth it.