We are not normally talking high carbon quality steel for broadheads. If the steel is soft, as most broadheads are, they will dull quickly if allowed to rattle around in a quiver. Unless they are stainless, the edge will oxidize as Mike Faith said. What makes them shaving sharp is that one molecule thick edge of the edge. When that oxidizes, what was shaving hair a week ago, may not do so today. A lot of inexpensive knives exhibit exactly the same thing.
Sharpen them, protect them from oxidation with an air-tight coating of wax, lip balm, grease, something and don't let them rub against anything.