Why IPv6? IPv4 is exhausted
IPv4 has 32-bit addresses — only ~4.3 billion unique addresses. In January 2011, IANA gave out the last IPv4 /8 blocks. We've been running on fumes (NAT) ever since.
IPv6 uses 128-bit addresses — 340 undecillion (3.4 × 10³⁸) unique addresses. Every person on earth could have 4.8 × 10²⁸ addresses. No NAT needed.