Sorting options depend on how the images are stored. When the images are kept in the file system, the app can sort them using information that is immediately available, such as the file’s creation date. It does not sort by rating or EXIF data because that would require opening each file individually, and doing so again whenever the data changes.
In the Photo Library, sorting is limited to the options that the library itself provides, which are based on date (created, modified, or added).
Both approaches work this way because the underlying database — whether it’s the file system or the photo library — can sort far more efficiently than having the user interface manually scan through every image.
I could add additional sorting choices, but doing so would significantly slow the app when working with large collections. I learned this early on while developing Nitro, where I initially included more sorting features but eventually removed them due to performance issues, especially on iPhone and iPad.