No one noticed the bug (or, alternatively, cared that it was visible).
It's been reported for months and hasn't been fixed.
A report earlier this year claimed that Apple was postponing some of the major features it had planned for iOS 12 in order to concentrate on fixing bugs in the code. That might be for the best, but it's an indictment of Apple that it let things get into such a mess in the first place.
Just over the past few weeks of the year, we saw both macOS and iOS hit by several high-profile bugs. And what's worse is that the fixes that Apple pushed out caused further problems.
iOS 11.2 contained a HomeKit bug that broke remote access for shared users
And this is just a selection of the bugs that users have had to contend with over the past few months. I've written at length about how it feels like the quality of software coming out of Apple has deteriorated significantly in recent years.
I've said it before, and I'll say it again, bugs happen. It's a fact of life. But over the past few years, we've seen a serious decline in the quality and cleanliness of the code coming out of Apple. And while it's easy to make excuses for the many -- many -- visual bugs in iOS, it's also hard to escape the fact that a lack of care over the small things leads to bigger and more serious problems.
Here's what I wrote in December 2017:
"Apple owes a lot of its current success to its dedicated fanbase, the people who would respond to Windows or Android issues with 'you should buy Apple, because that stuff just works.' Shattering that illusion for those people won't be good in the long term, which is why I think Apple needs to take a long, hard look at itself in the run up to 2018 and work out what's been going wrong and come up with ways to prevent problems from happening in the future."