The great thing about a drive-in theater was that you could sit in your car, chat with your companions, eat, smoke, or do virtually anything without bothering any of the other moviegoers.
Drive in theatres were great because you could squeeze all of your friends in the back of a truck, bring blankets and pillows and watch movies and the night stars.
Not all of them are gone. I still visit one frequently. They are rare but some still exhist. I loved that they were outdoors. You can also actually talk and laugh while the movie's playing without people shushing you. I also love them because they bring back childhood memories.