1- Apple might not be interested in listening to its users but I'm sure other businesses are. Apple users are loyal customers who can pay twice for a piece of technology and some of them will happily spend a night in line to be able to do that. Most advertisers would pay big money to Apple to know who those people are and what they want; that information is like gold.
2- unfortunately advertisers aren't the only entity potentially interested in spying people.
I think its laughable that this money would be tempting to Apple when they have a business that almost sees customers buying 700-1000 dollar plus devices on an annual or bi-annual subscription, especially when the privacy stance is one of the core pillars of the marketing message.
There is likely no commercially viable business model Apple could adopt to sell that data that would be remotely worth risking a 60-70 billion dollar a quarter in revenue money printing machine. That information is practically worthless in the context of iPhone revenue.
Should iPhone sales start to falter, this is absolutely something I would consider a concern, but the iPhone has a long way to fall.
I can imagine a system that throws an extra byte or 2 on those "chats" with the cell tower, or even abuses the timing that it decides to reach out and check the tower as the method of communication.
The actual voice recording and processing tech is small enough that it could be thrown right alongside the actual phone, for pretty cheap, and could run entirely separate from the phone itself, maybe even having its own battery!
Or not be sufficient in both cases.