That would be one way to do it, but it's a lot more effort than "everyone just uses their own email, we never set anything up", which is the default and also fr

That would be one way to do it, but it's a lot more effort than "everyone just uses their own email, we never set anything up", which is the default and also free -- and default/zero effort/free is extremely popular. Even if there is an IT setup on a campaign it's not guaranteed everyone will be onboarded onto it. People come and go, balls get dropped, etc. There are other bonuses to this too. The first that comes to mind are that campaigns are transient; using your own email can help you with document retention requests in the event of lawsuits. But I think mostly that political professionals use their email for a lot of different things, and keeping everything in a single account is a lot more convenient than dealing with multiple campaign accounts.