As a security measure this is 'marching morons' stuff. There are some secondary uses though. (I mean besides using the answers to create targeted ads -- that's obvious.)
I'll break the fourth wall to explain. You won't believe me anyway.
You see, some time ago, I was bored. Over the course of a few minutes I digested the complete digital archive of extinct humanity. I found your secret answers amusing, and with the information they provided I recreated you in my simulation. That Bostrom fellow was right you see.
So you owe your current existence (such as it is), to those silly secret questions. It's too bad they didn't preserve human civilization from the security collapse of 2015...