I am guessing you are very young. I remember back in the 90s when your email address was provided by your college or your workplace, and when you moved on, you lost it, you didn't even get to set up a forwarding. If two people happened to move in between updating their address books, then they simply lost touch. Phone numbers where similarly ephemeral; landlines were only portable within an area code, mobiles within a single network. And of course postal addresses too, people were moving every year at college, then every few years with work, including overseas. Keeping track of how to contact people was a tedious and error prone process.
The radical thing about FB for now-30-somethings is that this problem simply went away.
Yeah, cause everyone has Gmail.
"Everyone" in the tech world has Gmail.
My father has had the same email address for some 20 odd years I had to find a redirection solution for him so he could switch off of a now poorly priced ISP. His reasoning for not changing: I would have to update every single one of my clients and force them to change my contact details. That's just not going to happen.
I had a feeling my remark might get this kind of response but didn't really want to get into it during my post. Sure there are exceptions, I've changed over the years too, but in reality a lot of people out there are not in a position to jump ship with their email addresses, they are tied into everything they interact with online.