I take it you never worked at the coalface of software development, then? Patchnotes are (in reality) way down on the list of tasks a developer has to do.
It might be different in theory (SPICE, Atlassian Toolchain, ISO9000 and all that stuff) which requires more or less a workflow that starts with well written and structured requirements, from which you derive a high level design document, from which you derive a component design document (in UML), from which you derive nicely packaged developer tasks. In which case you have all the documentation beforehand and the patch notes drop out of the system at the press of a button (or so the vendors of the toolchain would make you, or rather the software management, believe).
In practice, though
- customer requirements aren't worth the paper they're printed on since
- the real requirements come in when the customer tells you that "oh, we thought this should work that way, what do you think?" three weeks later
- which leads to the management asking the developers to make it happen, now, since sales promised the customer to have everything done by teatime
- which in turn leads to the developers discussing with the expereinced programmers how they can do it
- after which the developers ask the programmers what they had done last week so they can put it in the documentation and set up the tasks the programmers have completed two weeks ago, hoping that this doesn't collide head-on with what the customer thinks what sales told them
Patch/release notes get written after you have the software released, when you somehow find the time to actually run it and compare what you see now with what you saw two weeks ago....
Or, to put it in another way: why do you think there are so many software developmnent models, quality assurance chains and people making heaps of money on seminars and in-house support for software companies who got bogged down trying to follow those nice theoretical scripts?
And if you think management should write the patch notes.... well, management counts themselves lucky if they even know which software version they have just presented to the customer, don't even think about what that version actually does.
