Consider the counter-factual: what if 64 bits ended up being not enough?
Given all the effort that needed and still needs to be done to move from IPv4 to IPv6, if we eventually needed to move to IPv7/8 it would even more difficult given how much IP in general has/is pervading civilization.
It's better to have the extra addresses and not need them, than need them and not have them.
It's the reason why ZFS went with 128 bits as well:
> Some customers already have datasets on the order of a petabyte, or 2^50 bytes. Thus the 64-bit capacity limit of 2^64 bytes is only 14 doublings away. Moore's Law for storage predicts that capacity will continue to double every 9-12 months, which means we'll start to hit the 64-bit limit in about a decade. Storage systems tend to live for several decades, so it would be foolish to create a new one without anticipating the needs that will surely arise within its projected lifetime.
> If 64 bits isn't enough, the next logical step is 128 bits. That's enough to survive Moore's Law until I'm dead, and after that, it's not my problem. But it does raise the question: what are the theoretical limits to storage capacity?
* https://web.archive.org/web/20171118074243/https://blogs.ora...