Car with a battery issue

There was a wait for more than an hour at the rental center ..with only one staff attending for a majority of the time. The car was due for an oil change ..the next day after I had parked the car in my driveway it would not start at all ..the car battery totally died ..now how does that happen ..I got the key and locked the car ..shouldn't that have taken care of lights etc ..which btw I didn't even touch ( switch on or something ) and I checked after that the lights turned off after the car was locked ..also budget wanted to charge me like 100 bucks for a jump start request ..I got it done and also came to know the coolant level in the car was like super low ..That car had an issue and I was super inconvenienced for renting it ..only good thing was after several attempts to reach the local office of budget 30 min wait on multiple calls and informing them , they said theyvwould not charge me for the late delivery which. I was able to return the car around 1 hr late