Is it really fair to compare the exit of WhatsApp with Tumblr? Tumblr has been around much longer, is used regularly by a lot of people, and isn't too hard to monetise via advertising. WhatsApp was purchased by a giant with a lot of money simply to prevent it's competitors from getting it. Obviously WhatsApp provided a lot more value to it's investors but the comparison just doesn't seem fair to me.

Edit:

It's also important to realise that our idea of a huge exit has changed rapidly over the last few years largely because of Facebook. A couple of years ago Instagram's $1bn astonished people. And yet Tumblr's $1.1bn isn't considered huge?