If you delete your account, facebook still knows who you are, still profiles you, still tracks you. You may no longer appear as John Hancock in search results but you're user ~11213421433243 in their system, you're already fingerprinted. The account you deleted is still reporting to the mothership, you need to kill their cookies, their partner cookies but your computer, your IP address, your browser profile, your battery still report enough information for facebook to make a calculated guess about who you are.
By all means delete your accounts, but you need to go a bit further to truly leave.