presumably so that if you start shouting about the heart attack you are having, that you dont need to wait until the end of the prerecorded message to get routed to a human operator
im not sure if you've ever been in a panic-filled emergency situation and had to dial 911, but the easier and more adaptable you can make it, the better. requiring button pushes, or anything else other than voice, should be avoided if possible.
this comes across as one of the best possible use cases of ai to me: only used in strict circumstances when human operators are busy, with the goal of deduping calls and reducing 911 queues.
and its been working really well, from the looks of it, for 3 years now