There's noting "smart" or "intuitive" about a backup function that, by default, chooses to back up nothing. Most users would end up turning on iCloud backups, and then get a shock when they need to restore and discover that, no, backups weren't really turned on... because they had to turn it on, then turn it on again for each individual app.
Quite the contrary, I'd bet that most people would likely prefer that it defaults to backing up all app data, and let the user decide - if they want to - to specify app data they don't want backed up.