Most likely because original authors were laid off or moved on; it's cheaper to rewrite software than to fix existing one; both need very different skillset and there are more people that can write their own algo quickly than fix somebody else's.

That's a very shortsighted thought, because the rewrite has also introduced its own set of new bugs.

Again, the cynic in me can't accept the "cheaper" argument. Apple has lack of funds to properly hire people who are not afraid to go into complex existing code? I get this argument in a start-up environment, but won't accept it in the case of the largest tech company in the world. This is just bad management.

Also, developers in their nature like to rewrite things. There should be a product owner overruling them. I’m saying this as a developer myself. Otherwise you end up in a situation where images are running the asylum.