See last point about backwards compatibility. Arrays did come later.
The array style probably should always be used nowadays (don't forget you also need to insert it into the command like ${args[@]}), but I learned before it was common (possibly before it was a thing, I'm having trouble finding exactly when basic arrays were added to bash) so I still use the string style when I know I won't need it.
The array style probably should always be used nowadays (don't forget you also need to insert it into the command like ${args[@]}), but I learned before it was common (possibly before it was a thing, I'm having trouble finding exactly when basic arrays were added to bash) so I still use the string style when I know I won't need it.