This can be reflected back with another question: Is it more important to provide an AP experience to all those who want it, or is it more important to provide a quality AP experience to some of those who want it?
Really, it isn’t a simple matter of shifting resources around. Teachers aren’t all omniskilled chess pieces to be moved around at whim—as human beings, they each have their own strengths and weaknesses. Some teachers may be excellent at teaching regular US history, but wouldn’t function as well in an AP classroom; others may be the exact opposite. There may be a number of teachers in a school who are certified to teach AP biology, but really aren’t that great at teaching the life sciences, but would be simply amazing at teaching an AP physics course. And so on.
Principals and school districts have to work with the skillsets their teachers have when scheduling and filling classes. And yes, they should also provide opportunities for teachers to increase their skillsets, but (a) that takes years to bear fruit and (b) it may not take with some individuals, anyway.