Abstruse
Legend
It goes back to "rulings over rules". If you want to play the game where every player keeps rolling over and over until they get two 18s, that's your game. Rather than creating complicated language to prevent it, they're letting DMs choose how to run their game.This will only work if we assume that the DMs will make players keep the first character they roll. In my experience that just doesn't happen. The other problem is the internet has taught me that people will cheat when they roll characters.
I look forward to someone asking wizards what happens with their attribute boosts they get from leveling when the character's attributes are already maxed out at 20.
The roll option is also a bit of pandering to old school players to draw them back in, to be honest. The way the system's laid out now, Roll > Point-Buy > Array in terms of total bonus, and Roll gives you the chance for a natural 16-18. At the end of the day though, the best it'll give you is +1 to a roll for a few levels before the rest of the parties come up.