The urgency of IPv6 adoption was predicated on the assumption that every connected device, both server and client, needs a unique and stable IP address. Back when IPv6 was first discussed, you couldn't even host two HTTPS sites on the same IP/port combination! That was such a colossal waste of IP addresses.
Another thing that changed on the server side was that, thanks to AWS and the like, it became trivial to set up a massive private network. Nowadays you can have a cluster of thousands of virtual machines that communicate with one another entirely within a VPC. Only machines that need to communicate with external entities get a public IPv4 address. This kind of setup not only frees up a /20, but also has the benefit of being more secure.
Meanwhile, on the client side, the rise of mobile internet means that devices can no longer assume that it will have any given address for any length of time. Even if we had plenty of addresses to go around, like with IPv6, what can we do when the device moves across the country? It's easier to assign a new address than to try to route the old address to an entirely different ISP. Reducing the complexity of the routing table was one of the goals of IPv6, after all. Insisting on a unique and stable IP address for each mobile device would defeat that purpose.
As a result, most new applications are being built with the assumption that the IP address doesn't matter. You rent a few ports on someone else's IP for a few minutes to fire off a bunch of requests, just like you'd rent CPU cycles on someone else's machine to run some functions.