A lot of people freaked out a few years ago when Doug Pederson started doing this. Now, it's becoming more common as coaches accept it (TB did it on Saturday), but I still see folks protesting. I heard a good explanation of the math today that hopefully makes more sense.
First, it's only valid if your team is able to get a 2nd TD without the other team scoring, so that is the assumed scenario. Also, for simplification purposes, assume that an XP is 100% probability and 2Pt conv is 50% (both are slightly less but that isn't too critical). Also must assume that winning in OT is close to 50%, so this may not be applicable if your team is a heavy favorite.
Option 1: Kick the 2 XPs, go to OT. Probably of winning = 50%
Option 2: Go for 2 on the first TD. There is a 50% chance that you win the game right then and there (remember, we assumed that you will score again and kick an XP).
If you miss it, you still have a 50% chance to make the 2Pt conv on the second TD and then a 50% chance to win in OT. The probably of this scenario playing out is 50% (that you miss the 1st 2pt conv) X 50% (that you make the 2nd 2pt conv) X 50% (that you win in OT) = 12.5%.
Going for 2pt conversion leading to a total probability of winning the game = 50% (make the 1st 2pt conv) + 12.5% (miss 1st 2pt conv, but make 2nd and win in OT) = 62.5%