That’s actually a choice made by the service. The onboarding document has the options listed and they get to choose, which is imho stupid. Just offer all options.
Service A has email enabled, service B doesn’t. Since ACM/IDM is SSO you can first authenticate with service A with your email code and then go to service B already authenticated.
I’m not even American and I knew who he was. For years I’ve been seeing memes about his face to head ratio and his gummy teeth.