I very much agree with what you said. There's absolutely nothing wrong with a hobbyist not wanting to understand everything down to the deepest level. I get really annoyed with the professional electrical engineers who want to force everyone else to learn as they did. If that's your career path then of course you will need to understand how to write your own debouncing code but for a hobbyist trying to get their project finished in some limited spare time it's not necessary and just acts as a barrier. If you make things too complicated then the people who are casually interested in this stuff will see there's too steep of a learning curve and do something else. That's the genius of the Arduino project: Make it as easy as possible to get started with microcontrollers while still allowing the potential to achieve professional quality results. Once you get hooked then you can always go dig into that debouncing function's source code to see how it works or write your own using direct port manipulation, assembly, etc.
It's possible that the Arduino team will consider your proposal and there has been no official response because they're busy and it's not a high priority. The best way to push it forward would be to submit a pull request to the Arduino AVR Boards hardware package, which is located in the Arduino IDE repository. The most important thing is to determine whether this will add any overhead when the function is not used and add that information to the PR as that will be a primary consideration. If that is accepted then function(s) with the same signature will need to be added to every other core library to keep the API consistent. The documentation will also need to be updated. This will require quite a bit of work from the Arduino developers and also 3rd party hardware package maintainers. You can reduce the amount of work for them (and thus increase the chances of it happening) but doing as much of the work as possible yourself but even so they will be responsible for reviewing all proposals, merging them, and maintaining the code in perpetuity. It's best just to start with a single pull request to the Arduino AVR Boards core library as this is used somewhat as a model for every other core but it would be a good idea to state your commitment to contributing to further work that will be required in the pull request description.
As you can see, it's so much easier just to write a 3rd party library, which requires no approval or effort from the Arduino developers, no long drawn out discussions/bike shedding on the mailing list, etc.