Forest fire management

In forest-fire management circles, controlled annual burns are generally considered good practices because they apparently decrease the fuel load as it builds, preventing large build-ups and then large, uncontrolled fires. My question is, why would there be a large buildup of fuel loads if they weren't burnt? Wouldn't the decomposers (termites, wood boring beetles, etc) be doing their jobs and returning deadwood to nutrients in the soil and carbon?