can someone explain how this isn't the intended behavior?
I don't think anyone sits down and thinks the intentional behaviour should be "we should make it easy for someone to send a notification email to 400,000 people". That would clearly be annoying.
I think the behaviour is accidental, arising from "notifying all people in a team is useful".
What about requiring people to join a specific team to access the source for no apparent reason? In other words, how are the conditions which led to the creation of this inflated team not antisocial as well?
it isn't for no apparent reason - it's to accept the terms of the agreement for access to the unreal source code.
Alright. So if Epic Games are abusing Github Teams, why should the poster not be able to also?