Prescribed burns are a good tool, but they're not a silver bullet. Because of the decades without fires, there's so much debris that fires burn incredibly hot, so you either need people to go in and thin the debris (this is actually a thing they do, as ridiculous as "cleaning the forest" sounds), or deal with the extra damage and risk of a very hot fire. Then you need a decent amount of personnel to make sure the fire doesn't get out of hand (and they regularly do), and do it when the weather is right (wet season, low winds). A prescribed burn is still a forest fire, with all the risks, it's just one that's started at a time and place we control.