I think it shows how difficult it is to ship a seemingly easy thing inside the Apple machine.

I'm more interested in how or why this bug was approved up be worked on so quickly after it was surfaced, rather than other longstanding and arguably more impactful bugs.

It's because the bug got publicity. Apple marketing prioritizes what does and doesn't get built. Someone saw bad publicity on the front page of HN and requested a fix.

The answer is probably a ho-hum combination of different teams work on different issues, and this one having annoyed one of the devs who could work on it.