And why exactly do you think they want you to change your wallpaper everyday?
Just because the option exists, doesn't mean you have to use it.
How does changing a wallpaper equate to there being a spy function?
Why would changing a wallpaper wear out a phone?
Also, unless you are pressing down on the screen, you should not even get the option to change it. If you are doing something to bring up the option, why is Apple in any way responsible for that? Stop pressing down on the screen, and you won't get the option to change it. If you do get it, you are free to not change, and entirely ignore it.