Answer in one word: Curiosity. I kept hearing about and getting messages inviting me to stuff on Facebook, for which I needed an account or site or whatever it's called, so I figured I'd check my inclination that it's a pointless time waster against the empirical evidence to see if it proved otherwise. I figured that (within reason) I'll simply press 'yes' rather than 'no' when things come my way -- as they were in increasing amounts -- and see where that leads me. I figured that might even help me determine whether it's a purposeless tool, a tool with a purpose, or simply a new means by which tools can amuse each other.
I guess I'll find out. If you're so inclined and you're of a mind to find my page or site or whatever it's called, then I'm sure you know how to go about such things.