But in reality their departure is really part of the business of software, the founders sell out, become exceedingly wealthy. After a few years the disillusionment with being part of a corporate machine (and not in control) sets in and they quit to spend time on their burning man floats. Its always been this way and theres nothing wrong with that.
I think many of us would do exactly the same given the option of struggling for a decade to profitability or a $10m+ exit with a comfortable VP level role.
I find it interesting that Instagram would want to include more adverts, as I find myself drawn to brands/interests without the help of annoying ads.