This is due to wallet software using more and more addresses, more sophisticated mixers, and proof of concept services sending thousands of microtransactions between them. This number does does not correspond to people, at least not suddenly at the scale indicated in that chart.
You have been under that rock for too long. This discussion has already been held without you. For example, what about all the offline transactions because of Coinbase and Changetip?
Partly because of the blocksize and confirmation times it makes no sense to settle each micro transaction on
the blockchain. The (indirect) real usage of Bitcoin has increased dramatically over the last two years.