To avoid NAT. Every device on your network needs a s̶t̶̶̶̶̶̶̶̶̶̶̶̶̶̶̶a̶̶̶̶̶̶̶̶̶̶̶̶̶̶̶t̶̶̶̶̶̶̶̶̶̶̶̶̶̶̶e̶̶̶̶̶̶̶̶̶̶̶̶̶̶̶l̶̶̶̶̶̶̶̶̶̶̶̶̶̶̶e̶̶̶̶̶̶̶̶̶̶̶̶̶̶̶s̶̶̶̶̶̶̶̶̶̶̶̶̶̶̶s̶̶̶̶̶̶̶̶̶̶̶̶̶̶̶ stateful connecting tracking system called NAT. All the devices share your single static public ipv4.
Many RTP, UDP protocols hate the idea of NAT and had to create several work arounds over time to work with it. Ipv6 eliminates the need for all that, and has the potential to greatly improve routing and latency. It's tbh long overdue and the excitement is that it's finally happening.