I'm not sure about iOS developers' intentions, but the better question is why would you make a filesystem case insensitive. Historically, making filesystems case-insensitive was a mistake.
There are some good discussions on the subject:
https://drewthaler.blogspot.com/2007/12/case-against-insensitivity.html https://news.ycombinator.com/item?id=8876722
To summarize
- It's poorly defined (think unicode).
- Every filesystem does it differently.
- Case-insensitivity should be handled in the UI layer.
- Case-insensitivity forces layering violations upon other code.
- Case-insensitivity is contagious.
- Case-insensitivity can lead to security bugs.
- Case-insensitivity adds complexity and provides no actual benefit.
In my opinion this is a good enough argument to make the filesystem case-sensitive.