Why are we so incompetent?

Here's a message from the Wiltshire Police website posted yesterday:

"There is Marlborough jazz festival being held this weekend....the main road through Marlborough is closed...Pedestrian access only for the weekend. The roads in and around Marlborough are gridlocked. There are approx 2 mile tailbacks all ways. People are getting someowhat fractious in the heat. Please try and avoid at all costs unless necessary."

All elements of this problem are predictable, We knew the MJF was scheduled for this weekend. We knew how many people were coming, and how many of them would come by car. The effect on local roads was predictable. The weather was predictable both generally (July can get hot) and more precisely over the last week (heatwave in progress).

So why did nobody bother to consider and resolve the problem in advance?

Picture - Police and Crime Commissioner Angus MacPherson (Con)