Mostly because I still charge outdoors. I am taking my time to get the fence extended so I can get a shed built to store all of the junk from the garage. Hence, I try to unplug if it looks like it will rain, or for overnight if I do not need a full charge--I do not like the idea of leaving it out for the neighborhood kids to mess with. On the few times that I need a full 10 hr of charging, I have left it plugged in without incident.
Also, with the high heat, I am guessing keeping it undercharged a little may be better for the battery (but, I do not have any reasoning to support this). Keeping in mind, too, that it is a 16kw battery, and the car charges up to 10kw.