Back when I managed a Blockbuster Video, most stores ran at a loss thanks to theft.
The real reason most stores failed wasn't because DVDs were going out. It was because we couldn't stem the flow of money out the door thanks to thieves.
Did they have the actual disc on the shelves? Where I'm from the rental places only displayed the cover, then you picked up the disc at the counter. Not sure how theft would've been a big problem then?
They moved to a system where it would just auto-sale you the title if you kept it too long after the due date, which people were furious about when they showed up with a title that was due back a month ago. Netflix really ate their lunch though, Blockbuster online was too little too late.