Technically this is because Linkedin asks to be given access to a user's contacts (phone, email or otherwise) and then displays the contacts as people possible

Technically this is because Linkedin asks to be given access to a user's contacts (phone, email or otherwise) and then displays the contacts as people possible to connect to, regardless of whether the contacts are members already or not. No doubt some manager with shady ethics thought this a very clever way to expand the number of users.