Of course they will commit to open source projects if it suits their needs (if they use those projects). But people have different opinion on what Apple's needs are.
Judging by the Engineering account being used to submit this patch, this is likely to be an example of the latter.
What does exist is specially "blessed" FAANG teams who are cleared to contribute to specific open-source projects that are critical to the business. Amazon has a team who contributes to the linux kernel for hypervisor support, for example.
It’s better than bitching about bad support without doing anything. But at the most fundamental of levels it’s really the company working for their customers, through a third party’s project.
So in practice, not very often
I’m perfectly happy to celebrate win-win outcomes.
You are aware that there are more than two options?
“Hooray, you did the thing you’re supposed to do. Good job you”.
Even when restricting that to “open source projects that (cl)aim to run on latest MacOS”, I think that’s not something a vendor is “supposed to do”.
So, if Apple only “is supposed to” support some projects, what objective criteria should it use to pick them?
I think it’s completely fine if Apple wouldn’t support any open source. I also think it’s completely fine if developers would choose not to write software for their OS because of that.