Why is there no "All Junk" folder in iOS Mail?

A folder called "All Junk" that combines all the junk mail from different email accounts into one convenient location has existed in the Mac OS Mail program forever...

...but it has never (to my knowledge) existed in iOS. I would very much like to see this option available for times when I need to quickly sift through all my junk mail to search for messages that may have fallen through the cracks.