Bootup screens in video games are nothing new. Here’s a page that goes into detail. Quoting a couple of the reasons:
Requiring the user to press start gets you a key piece of information: which controller is the primary controller. It’s not necessarily the first or only controller connected, and you might have several equally valid controllers to choose from. You don’t know which one the user has actually picked up though until they’ve pressed a button on it. Once that controller is used, it will remain the primary controller for the rest of the gameplay session.
This is required by the console manufacturer as part of the standard Technical Requirements Checklist (TRC). One reason is to allow the startup screen to loop back to a demo mode if no one has touched the controller, this stops screen burn and makes it easy for a store to simply pop in a game and let it run looping action with no intervention.