I suspect it's because you're not fighting monsters strong enough to penetrate the physical defenses of either armor. If that's the case, then the only difference between the two, in terms of defense, will be the magical reduction, which the scale is much better at. Top end defenses are not necessarily important either. Look at the min, average, and range to get a better sense of what will happen. Especially if magical monsters are doing something like 40 damage, they can do 0 to 40 damage to you when you wear the chain, but they can only do 0 to 7 damage to you when you wear the scale. It is a vulnerability of scales and chains (for magical damage) and robe and padded (for physical damage) that even very weak monsters can do damage to you at all, because the bottom of the range is always 0.
When taken on average, the magical defense of the chain is 42.5 and the magical defense of the scale is 66.5 so even on average, the scale has over 1.5 x the magical defenses of the chain. However, against much stronger monsters, the physical-skewed nature of general monster composition in this game may cause you to favor the chain. Which armor type provides the best defense between leather and plate is really situational and can change within a climb and depends heavily on what you are attempting to do. So don't write off the scale as being "better" just because it is better in this instance! Gl
