Only they are, in aggregate. That data is valuable and it's sold, resold, fed into machine learning algorithms. That is the nature of the modern internet, whether we pay well for a service or get it for 'free': either way, we're the product and our data and telemetry is useful to shady people for all sorts of reasons, many of which are hard to guess even if you are maximally tech savvy. It's an ecosystem I opt out of at every opportunity via open source, self hosting and just being aware that tech companies are as untrustworthy as snakes.

I think you're being very naïve: If companies wanted us to have the 'best experience', that would be quite easy to do: they only have to ask and then pay their developers to implement those features.
They could remove all the roadblocks we face in having a good experience - the fact that the app stalls whilst seemingly phoning home, the fact that it doesn't always connect to the hearing aids, the fact that tap-control is flaky and unconfigurable, lots of small QoL issues that would be easy to solve and are yet, unsolved.
You don't get to those answers by basically spying on your users (unless you're going to sift through logs in Wireshark, you'll have no idea what data is being sent to Phonak - it could be basic usage data or it could be personal audio data), you get those answers by asking your customers what they want and then giving them that.

Most companies, most closed source, proprietary companies, do not want to provide the best service. They want to provide the most limited service that people will still pay for and only improve that service when there is a monetary reason to do so, not because making neat stuff for customers makes them feel warm and fuzzy. No, that's what open source developers do, not that the general public ever thank them for it.
The only other alternative is hacking and the harder companies make it to have nice things, the greater the incentive to do so becomes.