No one cares anymore.
Everyone sits on giant balls of mud and those who built those balls are long gone. Fixing any of this would mean wading through and fixing endless legacy code at the risk of introducing new bugs. Some of it has hardware and radio broadcasting quirks involved which probably narrows down the people capable to understand the problem to almost 0.
And of those 0 people, no one gets promoted for fixing the incredibly buggy AirDrop. No one even knows how to replicate those bugs. Some iPhones in the wild sometimes stop being able to be found by other iPhones in the wild. Yikes. How do you even begin? Who's gonna write some debug code for a debug app for an iPhone in a lab and then runs back and forth with 50 other iPhones that also need to run debug code to finally get one in the state where it's unable to find or be found and then check diagnostics the communications hardware returns only to find out you need more diagnostic code.
Sync issues? Yikes again. Who the fuck would want to touch a system where any new bug could mean the destruction of trillions of photos and the wrath of OVER A BILLION of users. Flaky connections, many clients, sync algorithms, space on device limits, quota in the cloud limit, offloading of images. Also, once again, how do you even reliably replicate this issue which sporadically happens and sporadically resolves?
At scale and beyond critical mass, love and care and quality software are not rewarded. They are extra costs, just like human support agents.