Because BCC is so terrible at planning ahead and budgeting that they proudly parade their below-inflation rates increases every year, and then act shocked when an emergency comes around and they have no ability to pay for it!
Doesn't help that they spend such huge amounts on terrible congestion-creating projects like the Moggill Road Corridor Upgrade Project, and are forced to spend so much on basic road maintenance because they refuse to seriously plan to encourage people to get out of cars to reduce the load on roads.