It's more than just code. A "real" computer lets you do so much by piecing together work from different applications. For example, you can use a text editor like vim to transform a CSV file with powerful tools like regular expressions and shell commands, then load the CSV into your spreadsheet to work on. Yes, you can use the files application on iOS to manage your files but all of the other applications tend to stick to keeping all their files in one place.

On iOS it's very hard to build your own custom workflow with a bunch of applications and other tools, the way you can on a desktop OS.