What I believe these graphs are showing is the sentiment on a very short timeframe ,but longer term I believe some of the reasons are :
One main reason buyer interest was lower during December and January was the chinese announcements forbidding 3rd party payment processors from working with bitcoin exchanges ,the deadline 31st january ,so large investors are reluctanct to enter the market till after this deadline .
Second ,news that the FED are holding a very large quantity of bitcoins from the silk road closure ,until large investor know with some certainty how these will be liquidated they will stay on the sidelines .
I believe these below reasons are possibly reflected in your timeframe .
We have recently heard of MR Shrem being arrested for alleged money laundering adding further uncertainty.
We have also seen speculation recently that MTgot has issues leading to yet further uncertainty .
Until we see more certainty with the above issues new large finacial investors on the scale of Fidelity are going to be wary of investing ,these types of institutions are what will drive price higher .
My personal opinion is to buy a bit more bitcoin on bad news and reap the rewards later ,the only news you should sell on, is that there is a flaw in the bitcoin protocol ,all other bad news is an opportunity to lower your dollar cost average to maximise gains .
It would be interesting to know which exchanges or what individual exchange you gathered this data from ,we know to disregard gox since you can only buy coins there ,so bitstanp,BTC-e or perhaps some others may be a better reflection .
