https://www.reddit.com/r/linux/comments/jbzd85/cups_has_been_forked_after_apple_supplied_only/
CUPS has been forked after Apple supplied only one commit in all of 2020
CUPS was almost entirely made by Michael R Sweet who left Apple close to a year ago and now works for his own company.
Completely understandable to move the upstream repo away from Apple, I don't think there's much else to it.
He's been very active in the fork AFAICT.
His Sponsors page: https://github.com/sponsors/michaelrsweet