IPv4 addresses are now in short supply and ISP’s are becoming more and more protective of their allocations.
In the past businesses would just order large blocks of IPs, in case they needed them. Because there were so many, they were just given out. This has caused a large redundancy problem, and IP’s are now in short supply.
With NAT (Network Address Translation) and PAT (Port Address Translation) there is less of a need for organisations to order/require large blocks of IPs. The determining factors for IP allocation to different devices and services have changed.
When you request a certain block request size, many ISP’s will be quite demanding on what you want them for. They will investigate the equipment/services you want to allocate them to, and whether you have considered NAT/PAT to get round the need for a large block of IPs.