Why do I need an Egress rule when using a public loadbalancer

Summary

Public Load Balancer requires an explicit egress rule

Content

I have 0.0.0.0/0 as a stateful ingress rule allowing port 80 on both Public Subnets that contain the web servers for my back end set. In order to make the public load balancer work, I had to add an egress rule to allow egress on port 80 from both of those public subnets.

Shouldn't the fact that I had a staterul rule automatically allow the egress in response to a web request from the loadbalancer?