You can slap ads on anything. But the chance of slapping enough ads on a service to earn a multiple of a £130M valuation is pretty slim at the best of times, and when it's part of a trend of new "social" apps whose distinguishing feature is that they don't have network effects or targeting...

VCs backing startups whose primary hope of a major return is to get enough eyeballs to make Facebook nervous enough to buy them deserve to take losses more than most.

What the op is saying that nobody has yet worked out a way to monetise anonymous messaging. I can think of a few ways that it could be done (none ethical), but the major problem is that as the barrier to entry in this market is so low it is hard to prevent your user base defecting if you try. There is little network effect and no content ownership by the users to prevent them walking away.

notahacker beat me to it, but how do you sell ads to an anonymous audience without compromizing the anonymity of the audience? You can't, unless you want to do cheap, dumb banner ads. They missed the chance to monetize up front by launching as a free app. Any investor who looked at this app and thought for more than ten seconds should have run screaming, or had security drag the founders out of the building. Or both.