Yes, the justification was to discourage vaults that weren't ready. Say a L8 gets up and does a tsuk to her face for her first vault. Clearly, she doesn't want to count that score. She is going to do a second vault. Rather than risk a "O" for another tsuk to her face, she will vault a FHS and take the lower start value but at least get a score. Another option, a gymnast gets up for her first vault and does a decent tsuk. Rather than trying a second which might score lower or land on her face, she just stops and takes the first score.
Pretty much every coach I have talked to hates the new rule. From the judging side, it doesn't seem like it is making vaults any safer (just putting more pressure on the gymnast to make the 2nd vault count) and resulting in a lot of debate between coaches/gymnasts and one coach and another coach.
But, that's where it's at right now.