I forgot the lights on overnight on a 2016 Volkswagen Jetta and 16 hours later when I came back to the car the lights were still on but the car wouldn't start.
Can't the car check the battery level and automatically turn off lights if it had been stopped for a long while so as to prevent the battery from completely draining out?
As in, always keep a reserve charge enough to start the engine.
UPDATE two weeks later after reading all the answers: it makes sense to allow the user to leave the lights on even with they key out of ignition (e.g. setting camp, or locking the car while going to get help). But I can't think of any situation in which it would make sense for a car to let the lights consume so much battery power (presumably 8+ hours of continuous lighting) that the car will no longer start. Even if there were some such strange situation (watching snails drunk on molasses setting up camp during the arctic night), if lights go off automatically every, say, 6 hours without the key in ignition, I doubt any car owner would have a problem with turning them back on, but far more owners will be grateful they didn't have their morning plans ruined because they had to jump start the car after humanly forgetting to turn off the lights or not hearing the car beep for whatever reason.
Perhaps car makers have something to learn about battery management from smartphone makers.