Up until 1.21 the Bundle item was not locked behind the bundle experiment, only its recipe was. That's important because many data packs (such as the popular VanillaTweaks) added a recipe for the bundle to make it available in survival. Since the bundle experiment started receiving updates again, the bundle item itself is no longer available (e.g. via /give @p minecraft:bundle), which may be problematic when updating from 1.21(.1) to 1.21.2 eventually, if the bundle stays experimental in that version.