[crazy2be]

NAT has not solved the IP address problem, it has merely postponed it slightly. Multi-level NATs are a hell far beyond the single-level NATs that most consumers see (and single-level NATs already cause all sorts of problems for even moderately advanced network usage). So most people only have single-level NATs, which practically only extends the address space by a small multiple - 8 bits at most, in practice ~2-3 bits.

128 bits allows routing tables to be super small and fast. While RAM has gotten cheaper, it is still slow, and smaller routing tables are way more important than smaller addresses.

However, I agree with your central point - IPv4 was "good enough" that IPv6 is going to be a tougher battle than it ought to be. However, IPv6 is winning that battle already. 15% of google's users use IPv6, and it's increasing sigmoidally. [1]

[1] https://en.wikipedia.org/wiki/IPv6_deployment