A typical ISP will get allocated a much larger allocation like a /20, which allows them to allocate a /56 for each of their customers while still having a few bits to play with. But all starting with the same <isp_network> prefix.
With IPv4 you will have many separate fragmented networks that have no numbers in common. And this will only get worse over time.
However, SLAAC demands that each device is given a 64-bit prefix that it then chooses many random 64-bit host addresses from, without any other rhyme or reason. So, if you want to know the IP of a host you want to connect to, you have to remember at least a 64-bit number that changes every day by design. Add to that some extra bits for the particular part of the network you are in.
So your IPv6 is more like <isp-assigned-prefix, 32-56 bits>:<internal-net-prefix, 8-32 bits>:<random-host-address, 64 bits>. Human friendly this is not.
A machine using IPv6 privacy extensions would have two addresses; one that changes, and one typically based on the MAC address that remains constant.
If you are in the local network with that machine or otherwise are supposed to be in-the-know, you'd know it's fixed address and connect to that.