The welcome page is aimed at first time Ember developers to point them at some good starting resources. It isn’t intended to be part of your actual production app.
Oh I see - ember-welcome-page is not a frontend app - but uses Express middleware to replace index.html.
Learners, not being familiar with addon+serverMiddleware, might find it a bit disconcerting (“copy dist/ folder to your website”) does not give the same result as localhost:4200. I know I was surprised.
Perhaps the quick start guide should include a pointer that what you see in “ember serve” is due to Express+middleware and on a web server you will (correctly) see a blank page.