The MAC address is very important for developers. It tells them which GUI elements are accesed, what error messages are common and what features of the program are accessed.
For some reason developers think they're magically exempt from judgement of their data harvesting. I don't want you monitoring my activity on my goddamn devices, however much you yammer on about having good intentions. The act itself is hostile, and that's why developers are so goddamn sneaky about it. You're invading privacy and creating metadata records that are trivially deanonymized.
There's an honest, non sneaky way of gathering usage information: pay for rigorous testing and price the cost into the product. Telemetry is lazy, invasive, and user hostile by default. Every bit of information acquired from users should be given with informed consent or not collected at all.
From what I've seen the invasive data harvesting often does not come from developers themselves, but is rather requested by product and BI wanting to get more insights into the customers.
It's hard to really stand up to that kind of situation.
The important part of them having the MAC address is that it IS a unique ID. If it wasn't a unique ID, then it wouldn't matter if they had it, because their purpose in taking it is to identify you. So whether it's hashed or not is completely irrelevant.
The fact that they are taking uniquely identifiable information from you, and the fact that their company is as deep in the Ad game as Google, is more than damning enough.