Also the already stored data makes it quite the treasure. Even if every user instantly stops using it, it'll still be very valuable due to the existing data (if they keep it).
Too stray off-topic though somewhat on a self-created tangent: There's an app called Flitsmeister in the Metherlands (and abroad but several countries banned it) that keeps on growing. I wonder when they will be bought out. Not necessarily for the active social network behind it, but rather for the data that is already there. I believe such a vast amount of historic data is hugely valuable on it's own. I wonder by who, when and for how much they will be bought out.
"...we shared many of the same core values..."
Why not just say, "They made us an offer we couldn't resist. ( ͡° ͜ʖ ͡°)"
"When we met with Facebook, we were impressed with the huge pile of cash that they offered us. Most of all, it was very green and crisp, and smelled like cash it supposed to smell, so we were compelled by the ways this cash could help us realize our vision of getting rich."