Because people are still living in the 90s and even the best developers just love to gobble up Apple's propaganda bullshit.
That doesn't make Microsoft's double-talk okay, Apple never pretended to :heart: opensource.
But they did. They claimed part of Mac OS, Darwin, is open source. Like Google like to brag about Android being Open Source even if you have to put a ton of proprietary software on top of the open source parts to make it usable.
Apple didn't take ownership and then start closing CUPS, but they have also never pretended to be a friend of OpenSouce. They haven't produced anything opensource since then. There have been a couple of projects, like their rebranding of KHTML that suited their purposes but they never donated time or money back, or even pretended to help upstream.
If you look at the Asahi Linux on M processors, Apple don't hinder and may have arguably done things in a way to not block them but they certainly have not helped or even claimed that it was a good thing.
Two counter-examples:
They open sourced Swift in 2015 (https://en.wikipedia.org/wiki/Swift_(programming_language)#H...), and Swift-DocC in 2021 (https://www.swift.org/blog/swift-docc/)
Apple bought CUPS in 2007 (https://en.wikipedia.org/wiki/CUPS#History)
Except dot net devs. Which is the point.
CUPS was critical infrastructure for Apple, so they bought it. Since it is GPL they couldn't close it, hence they abandoned it.
Apple are not your friend, but they never claimed to be, you just might have an overlapping interest, Microsoft hold big "We Heart Linux" events.
I think I clearly showed they have.
The vast majority of iOS developers. Swift 1.0 wasn’t open source, and IIRC when it was announced there wasn’t even a promise that it would be open source. I think Chris Lattner did signal they were willing to seriously consider it some time in the future; that was all.
There is a lot of money to be made in iOS, so people will use whatever Apple forces them to use, whether it’s open source or not. If some would leave money on the table on ideological grounds, all the better for everyone else.
If anything Apple offered Solaris, Irix refugees a viable desktop transition.
The proximity with Linux was an accident. NeXT is from the late 80s, pre Linux, and NeXT was the baggage OS X had to work with. They didn't strip out the Unix parts, but also didn't widely proclaim it was "close to Linux". It was mostly the developer community touting it as an advantage of macOS, with Apple later admitting "yeah yeah that's also cool" and later shipping Python and Ruby alongside Perl just for completion.
Even when Apple clearly tried to help Homebrew by offering a Xcode-less toolchain there was not even a peep about the purpose of "Command Line Tools". It took them years to acknowledge it existed.
Also, like the sibling response said, Linux only started being as widely used later than OS X.
Just check StackOverflow 2021 survey - Swift is like 5%