This would be speculation, but I would think it has to do with the CSFB warning about bitcoin being the "wild west"
These kind of warning make it less likely that consumers will want to buy and use bitcoin as they fear they will get scammed out of their money. If less people buy and use bitcoin then the price will go down
Honestly, who listens to them? If I hadn't been following Bitcoin very closely, I never would have heard about their advice. I do think it's the cause of the price drop, but long term it should have little effect.