but we’re almost out of numbers.

We are out of numbers. Just because technically there might be some unassigned or even assigned but unused numbers doesn't mean we didn't run out of them. There are more devices in the world connected to the Internet than IPv4 addresses exist. If you read this sentence from the standard strictly:

The internet protocol provides for transmitting blocks of data called datagrams from sources to destinations, where sources and destinations are hosts identified by fixed length addresses.

This isn't the case with NATing as hosts are no longer identified be the address alone (but additionally other parameters like port number or TCP connection status). You can't ICMP ping a NATted host to my knowledge because it operates on IP directly (it's actually part of IP itself). So parts of the protocol become unusable. So just by logic, we have run out. The last remaining blocks won't fix the issue, and rather make routing worse than it already is.