Why did we do CIDR? (RE: Confussion over multi-homing)

On Thu, 14 September 2000, Paul Froutan wrote:

What you can do is get permission from the ISP that provides you the IPs (say ISP A) so you can have other ISPs announce your blocks. You also need to get ISP A to deaggregate your block and announce it separately into the global BGP table. We did this back in the day and it works fine if the ISP giving you IPs is somewhat reasonable and helpful.

If folks are going to deaggregate the addresses and announce multiple routes anyway, why are we going through the pain of ARIN policies. Wouldn't it be better to allocate the appropriately sized address in the first place?