FP+ had the unfortunate timing that if someone showed up on property clueless, their entire vacation was already hosed with no way of recovering from the lack of pre-booked FP+. "Oh! You should have booked these 30 (or 60!) days ago. Too bad, so sad, nothing you can do now. And nothing you can do about your park days for the next six days either."
With
Genie+, a clueless guest can become clue-full and use Genie+ for the rest of the day and for the rest of the trip. "Oh! you can sign up for Genie+ right now, if you want." or worst case "Sign up for Genie+ *tomorrow*"