As an example, activities include an "audio ducking option", the options for which in iOS 18 are: "Default", "On", or "Off". In other words, the new ducking modes exposed by the rotor haven't made it into the activities system, because it's isolated and fragmented from the rest of the screen reader.
It requires Apple to explicitly opt aspects of behaviour into activity readiness, and make a new UI for their configuration even though one already exists elsewhere. The result, unsurprisingly for something that relies on humans to put in extra work, is activities feeling like an outdated island, or a feature that's still very immature.