Why Reply?

I belong to a site on Facebook for people who went to South Oceanside Elementary School.  I was hoping one day, someone will write on it and I will remember going to school with that person.  When I left in the 80's, I lost all touch with any of them.  The other day, someone posted about a principal and the 4th and 5th grade.  I remember that guy.  I posted to ask what year and said he drove a Corvette.  You know what, I got no reply.  Why do people post things and don't reply?  This happens when we sell things online, also.  People inquire about it and then nothing.  Is it just a fun thing to do?   Are they just looking for certain replies?   I just don't understand.