It was the combination of asymmetric, no or few IPs (and NAT), and bandwidth caps.
let's not rewrite history here: IPv4 address scarcity has been a thing since the very early 1990s. Otherwise why would cidr have been created?
CIDR had nothing to do with address scarcity. CIDR was invented for routing table slot scarcity in Cisco AGS hardware of the era. Routers running out of BGP table space wasn’t just a fear at the time, it was a real problem on a number of networks, including, but not limited to SPRINT and MCI who were the big dogs in the fight at the time. NAT, OTOH, is an address conservation mechanism which has unfortunately of late been mistaken for a security tool. If only people would realize how much NAT negatively impacts security, manageability, etc. Owen