If taking another measurement requires climbing back up the ladder and reaching over to hook the measuring tape, the need for a third number to break the tie might seem less important. If cutting the piece of wood too short isn’t likely to be seen except by someone who’s looking for errors (in other words, doesn’t affect the overall outcome to a significant degree), but cutting it too long would mean it wouldn’t fit and thus require climbing back down off the ladder to make a second cut, a third measurement might not be worth the time involved.
In other words, as a former carpenter I’d say that motivated reasoning often affects the decision-making process. Shocking, I know.