But if they kicked the FG, then got the onside kick and scored the TD and missed the 2 pt, they’d need the ball a third time.
If they go for the TD now, go for the 2 pt, and see if they get it, then they know if they need a TD or a FG on the last drive. Makes it so they don’t potentially need the ball a third time.
I mean, both situations were improbable, but when you need the 2 pt you need to know as soon as possible whether you’ll need another TD or not.