Part of the reason is the way batteries work. Standard alkaline batteries have a higher voltage discharge curve then say lithium batteries. So actually when the battery level is down to say 70% it’s running low “power”, when I say power I mean the ability to draw amps from the battery. Now consider a deadbolt, it has a pretty heavy duty motor that draws a lot of power. As a alkaline battery at 70% when the motor tries to “draw” that enormous amount of power/amps from the battery the voltage takes a tank and this causes the electronics to shutdown the lock. On the slip side a FE599 which is a magnetic actuator lock needs far fewer amps to achieve a lock/unlock hence it can go onto about 50% when finally the magnetic draw on the actuator causes the voltage to drop and shutdown the lock.
This is one the reasons we wrote this SmartApp with a configurable low battery warning and groups so that users can setup thresholds for different devices and we’ve even recommended a few 
There is ONE easy solution to this, use 1.7v Lithium batteries (like Blink camera does), lithium batteries are FAR more stable/flatter in their voltage curves and this stability allows the devices to maximize the use of the batteries. So if you were to run your locks on a lithium battery you’ll find that the batteries last much longer and you can use them till they are almost depleted because of the flatter voltage curves. See this comparison I posted about Alkaline vs Lithium (note however that the DH would need to be recalibrated to accurately report the battery levels for lithium)