I remember signing up for Facebook back in the day. They tried to get me to share something about my email contacts list. That just made me not use Facebook instead. Unfortunately, everyone else didn't seem to have a problem with it.

Facebook literally had a box on their web site asking for your email address and email account password, so they could log in to your webmail and scrape your contacts.

Normal people value their social standing and their relationships, bragging rights etc. higher than abstract principles. It's only loners who will resist. Popular people will be on board because they manage their brand and image instinctively. Wannabe popular too.