Their ranges are running dry. Nearly all address spaces are taken, so we will need to migrate eventually.
However, since almost everyone still supports both, and ipv4 is much easier to read and maintain, adoption of IPv6 has been slow.
They went just a teeny tiny little bit overboard with the address space. Ipv4 is four groups between 0 and 255, ipv6 is eight groups of four digit hex, 0000 to ffff - e.g the Google DNS ipv4 address is 8.8.8.8. the ipv6 one is 2001:4860:4860:0:0:0:0:8888 (thankfully at least some devices allow using :: to skip all the zeroes, so it's "just" 2001:4860:4860::8888)
But we now have enough ipv6 addresses to give more than 10 billion ipv6 addresses to every single grain of sand on earth, and still have some left over.
They never wanted to worry about address space size again. And this makes subnetting much easier. I have a /56 allocation so I could do 256 /64 subnets. I hope that at some point home routers will have the option for seperate subnets built in. This way you could easily have guest, IoT, work or whatever networks without NAT.
One thing you have to consider though is that the minimum network size that allows autoconf is /64 and that because of the privacy extension a device usually has 3-4 IPv6 adresses.
we already have enough IPv4 addresses thanks to stuff such as NAT and CG-NAT, these devices also protect the end-user by not directly exposing their IP to the internet
what's the problem with broadcast? also afaik IPv4 also supports multicast
In my opinion NAT is a hack that makes lot of things harder than they should be. STUN and TURN are services that are created because there is no easy way to connect two hosts between different NATs. UPnP for port forwarding is another. CG-NAT is even worse. I have heard of so many people having problems with it.
Breadcast is messy. It is like screaming into a room and waiting for an answer. Multicast lets the computer decide if it wants and needs to listen to a specific group message.
IPv4 didn't have cidr from the beginning. They only had classes. IPv6 was designed with complex routing and sub routing in mind.
IPV4 has a static ceiling for how many addresses can exist. We're concerningly close to that ceiling already. If we were to run out, internet suddenly becomes a fucking nightmare.
Imagine getting out of phone numbers, so the solutions is for everyone to call the last remaining people with public/routable numbers 24/7 so those people would redirect messages to others.
With Internet, users does not see that easly, but if you host anything for others it's getting harder and harder to accept incoming connections without many layers of hacks to bypass hacks that ISPs do to keep IPv4 network working.