I do understand that global external addresses are used for External Load Balancers while regional external addresses for VMs and Regional Load Balancers. Why is there such a separation between global and regional IP?
They both can be reached from the internet. Is there implementation detail? Can somebody explain that?
Global IP addresses are different because of ANYCAST. The same IP address can represent more than one data center. Load balancers, DNS servers, CDNs, etc use ANYCAST and BGP (Border Gateway Protocol) to route the client to the closest datacenter using one IP address. You could imagine this as one global IP address can route to one of many regional IP addresses. Which regional IP address is determined by BGP (the routing rules).