It's a mental rule. Both teams had four quarters to try and win. But you get to OT and based on the flip of a coin one team has an absolutely massive advantage.
Comparisons.
Tennis matches decided by 1 play off game where you flip a coin to see who serves. Mental
Penalty shoot out in soccer where one team gets to take all their penalties first and if they score them all, the other team doesn't get to take theirs. They just lose. Mental
Darts matches decided by a closest to the bull but if the first player hits hit, he wins. Mental.
I know fans of NFL are defensive of the sport because it does come in for a bit of flack. But you can't defend that rule. A teams whole season comes down to the flip of a coin. It's madness.