I'm pretty sure that those who built new protocol were aware of this and were like "anyway we are gonna have to upgrade network devices. Why don't we build a new protocol while avoiding pitfalls of older one"
Any comittee that sat down to solve IPv4 issue would have thought of compatibility first.
I am shocked that so many people agree with OP's armchair solution here.
IPv4 w/ more bits is a lot more simple. Yes, older network gear wouldn't deal with it well, but that's not a real issue today because that same network gear supports IPv6.
Buuut, one of the biggest problems with app-level issues is just that the app doesn't bother dealing with IPv6 addresses and AAAA records. It would be the same issue with an imaginary IPv4*2.
96 bits would probably be enough too, but having large subnets has a few benefits -- it allows for securing NDP by using the extra space for a cryptographic key, and also it makes it much, much harder to scan for active hosts from outside the network.
Plus, can you imaging the wailing and teeth gnashing we'd be getting if v6 wasn't a power of 2 bits long?