Instagram was barely two years old when FB acquired them for $1B along with a promise to allow Ig to continue to operate independently. It'd be very hard for most founders/investors to pass up such a deal, particularly with an app that was even more of a one-trick-pony at the time.
SNAP was offered bucketloads of cash and refused. WhatsApp agreed to be acquired but now both founders are gone. The impression I get about FB from these stories is that its pretty much a Faustian bargain to join them...
