The pivotal event was the Nortel-Microsoft deal where a court overruled the IANA hippies and said that IP blocks look like property and quack like property so they must be property.
AWS charges $1/month or $12/year to sit on an IP address unused. This price / value pressure has freed up a TON of address space and pushed down pricing signals on a lot of ipv4 usage (ie, you can say is it worth $300M to buy a class A or maybe we should spend $200M to get IPv6 going.