A design that allows cells to routinely fall below "lockout" level, is ,IMO incompetently and poorly engineered. (Unless it's a deliberate and cynical ploy to sell more batteries ) but no firm would put profit before dependability,would they?
Routinely, yes. But one of the functions of the battery systems is to provide power in an abnormal (emergency) situation. In this case, its better to kill the battery by running it dead than to lose the aircraft.
The problem now becomes: How do you differentiate between an abnormal condition and some maintenance person leaving a switch on at the end of shift? Without incorporating a bunch of air-ground and other logic with its failure modes?