Last offseason, the NFL changed the scoring rules for overtime playoff games. Both teams must now get at least one possession (unless there's a defensive score).
So let's suppose you lose the coin flip, opponent chooses to receive, and scores a TD on their first possession. They kick the extra point. You also score a TD on your possession. Do you kick the extra point to extend overtime, handing the ball back to the opponent in sudden death, and ask your defense to get a stop? Or do you go for two and end the game, win or lose?
Too many variables. If my defense is not playing well I may go for it. If they are playing relatively well I might keep going to give them another shot at stopping them. The opposite would be true too if they had a great performing defense or one that was currently struggling.