Only because others you communicate with may not have ADP turned on, which is a flaw with any service that you cannot control what the other end does or does not do, not unique to Apple/iMessage outside of using something like Signal.

	▲	modeless an hour ago \| parent [-]
		Most other E2EE messaging services do not break their own E2EE by intentionally uploading messages or encryption keys to servers owned by the same company in a form that they can read. For example, Google's Messages app does not do this for E2EE conversations. This isn't something that only Signal cares about.