Preferably an inventory item editor, some quests involve you collecting items, although if you have max items and pick them up for the quest it doesn't register and count towards the progress.
Popularity of the title, complexity in adding the cheats, etc. Honestly you don't really 'need' more. The options we have are plenty enough. Though if there are specific cheats you feel are missing you can always use the request option.
Agreed on being able to edit the amounts instead of instant max. Had to revert a save due to not being able to complete a quest. Its a nice cheat, but can certainly break things once you've maxed out your stuff and have no way to decrease them anymore.