That applies to a zillion other parts of Mac OS X, too, but does that matter?
If it matters: to be fair, Android was around before Google's involvement and they purchased the source + hired the developer (1), and the Linux core of Android also wasn't developed by Google, IIRC.
(1) they probably did more work on Android than Apple did on CUPS, but that's a gradual difference.
It's always fun to remember a time when Mac OS X's printer support was so bad (mostly due to low marketshare) that they had to adopt the Linux printing solution, and it was an immediate and massive improvement.
And you try and tell the young people of today that ..... they won't believe you.
They bought Howl software, its developers, and renamed it Bonjour and made it open-source - that became the de-facto standard for their network "plug-n-play" support for devices because Microsoft was trying to convince standards groups to make its (failed) protocol the standard for this.
OSX printer support wasn't bad because of low marketshare. It was bad because it was a new operating system. And it wasn't just printers but everything. Drivers, applications, utilities. They all took years to move to OSX.
And most technologically astute people (young or old) know that OSX relies extensively on UNIX software of which CUPS is just one part.
"It was bad because it was a new operating system." -- it was already bad in the pre-OSX Mac era (mostly due to low marketshare).
"And it wasn't just printers but everything. Drivers, applications, utilities. They all took years to move to OSX." -- for applications and most other things Apple had migration alternatives (Carbon APIs for pre-OSX Mac apps, the Classic environment for emulation of pre-OSX and even Rosetta for emulating PowerPC on Intel).
For the case of printers, they really just dropped whatever they had and went with the Linux solution.