Thieves have attempted this approach for as long as this type of cash delivery system has existed, and consequently there are numerous security measures to prevent it. The ceiling space that contains the tubes is usually protected by motion sensors, the cash delivery system usually has some form of intrusion countermeasure that would detect a change in pressure, and the most simple method is a timer system that detects whether the money is received in the strong room N seconds after it's sent by the cashier, triggering an alarm if not.
It seems that for whatever reason this chain of stores hadn't implemented the basic security measures, or they were ineffective, probably due to human error (i.e. forgetting to set the alarm in the roofspace).