One issue is weather; In this part of the US drive-ins really only work in summer. Would you want to sit in your car watching a movie this past week?

Otherwise:

• Real estate here is worth more than the business. The places where the most people are would be difficult to operate.
• Comfort. While I had a drive in close by growing up (Circle Drive In, Dickson City, PA) it's something we'd do once or twice a summer. Granted, we took my father's truck with a cap, so we'd back in, bring foam/carpet remnants to make a bed, and I'd rig up a multi speaker system with a DC adapter with my Walkman radio for decent sound. I couldn't enjoy a movie sitting in my car.
• Timing: You have to wait until it's dark to watch a movie, which usually means 21:00 in summer. The one by me would start at 20:30 but it was hard to see the movie for the first 20-30 mins. Sure, on a weekend you might get some more viewers but during the week you're losing all the people who can't be out late for whatever reason.

Honestly I think the one-off or weekly summer events at the beach or on a rooftop in various places around the state in summer are a better solution than a dedicated drive in.