My question is why my keep asking me to backup to the iCloud

It's asking this so that you'll have a copy of your information to use in case your device is ever replaced, lost, or damaged -- How to back up your iPhone, iPad, and iPod touch - Apple Support.

I back up to itunes, so I don't want to back up to icloud. But it keeps asking me to. If I don't back up to icloud, my contcts go away