The new cars are more complex and have more modules (=computers) than ever. Some of the vehicles have 30 different modules and each usually has some parasitic draw to keep memory alive. When you add up all of the modules it is a fairly high number. Besides the radio which has memory, the clock, remote keyless entry that is on, and the list goes on. It is not that the batteries are getting worse, but there is more demand on them. Todays car does not have a mode where there is no draw on the battery.