“Every program attempts to expand until it can read mail. Those programs which cannot so expand are replaced by ones which can.”

If you'll allow me to riff on jwz, I think another law is applicable to social media:

"Every social media company will expand until it becomes a bank. Those social media companies which cannot so expand are replaced by the ones which will. A bank is meant in the sense that it will store and mantain things of value including favors, records, and money."