Comment by andix

Most consumer ISPs regularly rotate the prefix. IPv6 has proper support for that and can keep connections on the old and new prefix alive for a while in parallel.

With IPv4 most ISPs only rotate IPs on new connections (router restart). But my old home internet even stayed on the same ipv4 for years. Only if I shut down the router for a longer time it got a fresh ipv4 assigned.

So it's an implementation detail, not a technical limitation. Not rotating the prefix is a bad implementation.