To make up some numbers: Assume that a paint job lasts 20 years. So if it takes a team of five 20 years to paint the bridge by the time they've reached the end the beginning will need a new coat.

Otherwise every 20 years they would need to hire, train, then fire 200 painters for a 6 month-long paint job project. 200 painters, managers, and etc. who will invariably be less experienced with the finer points of painting said bridge since they don't do it every day.