It doesn’t have to be a park, it can be any public place to get out of the quiet office where it’s harder to find out which sound needs to be changed. One of the reasons why this is not done is because the configuration of hearing aids is insufficiently practical
I doubt that’s one of the reasons.
I’d bet that the main reason it isn’t done is that it would be beyond impractical for a provider to be traipsing around the countryside trying to find a specific environment that the customer wants to tune. How would they plan for that? How would that time get paid for?
Every audiologist (and really, every optometrist, family doctor, allergist, or other specialist) that I have ever worked with operates out of an office. That office has the tools and supplies they need to perform their services. That office also creates the convenience of knowing where to find that provider. The provider schedules appointments based on how many patients they expect to be able to see in a day, and I would imagine that number is based on their experience with the amount of time an average appointment takes.
Meeting us somewhere outside of the office might sound good to us, at least at first blush… but you are asking for adjustments to be made in an uncontrolled, unrepeatable sound environment. That’s not a good model.
I get just as frustrated as the next guy - and I have shared that frustration with my audiologists - about the unrealistic sound environment in their office. What sounds “good” in a 10’x15’ office when spoken by someone who has trained to speak slowly and clearly, doesn’t really help me in a bowling alley or restaurant. But they are a business, and have to be able to meet business goals. Or they won’t be in business at all.
Given all of that, the lack of a portable form factor for making adjustments in real time can’t be high on the list of hurdles that we face.
Luckily, the communication device for programming most current hearing aids is relatively accessible, and the fitting software for most brands can be found if you know where to look. Loading the software on a laptop will let you take it to the park, or a restaurant, or wherever you want - and make whatever adjustments make you happy.