The creator of CUPS was employed by Apple, to work on CUPS. He left, and doesn't work on CUPS anymore. It's not some cloak-and-dagger thing.
his fork: https://github.com/OpenPrinting/cups
Cloak and dagger? no
Terrible stewardship of an open-source project? yes
Surprising, given Apple's history? not at all
The last thing Apple did with CUPS is add functionality to allow legacy printers that don't natively support IPP to function as an IPP printer.
>Products using the Internet Printing Protocol include CUPS (which is part of Apple macOS and many BSD and Linux distributions and is the reference implementation for most versions of IPP
https://en.wikipedia.org/wiki/Internet_Printing_Protocol
Going forward, the Printer Working Group is in charge of IPP, and the creator of CUPS now works for them.