Police aren't going to follow every automated truck on the road. And a balance has to be found or PDs will ignore shipping companies. Too many false alarms; they stop responding.

So by the time a truck is stopped, realizes a robbery is in progress, contacts command, who assesses if it's a real event, who contact local police, who send a cruiser to check investigate. They thiefs could have gotten away with quite a lot.

Btw, a grand theft rarely rises to immediate action. City PD have bigger concerns, most of the Midwest is sparsely populated. That leaves the bored suburb PD who'll be in the most responsive.