Why would some one want to invest in something where they only get their money back in 10-15 years? sequoia capital turned 58M(8M in 2011 and 50M in 2013) into >$2 billion in whatsapp and 1.5B was made with the 8M.
How much profit does whatasapp make? Even God doesn't have any clue. Would they ever make profit, your guess is as good as mine.
The point you laid out is valid. However it's capitalism at its worst. By the way how many social apps get acquired for $1b or $19 billions ;) Most of them are a trap for VC, it's just few get lucky. It's a musical chair game but in the reverse order. Where your job is to put another VC in your place while you exit.