my opinion: peoples' sentiment, and overall bear market.
Some people predicted such long bear markets (Tone Vays, Richard Heart).
If you look at yesterday's video Ivan on tech and Richard Heart, mr.Heart summarises clearly that this all bubble burst was inevitable, as so many scam projects are around the space, and so many people who just got investors' money and not doing anything with the projects, or even worse some people used the hype momentum and attracted capital in form of ICOs and just"living comfortable life now", without developing anything useful, just little tweaks in their projects.
RE: What's the real cause of the decline in Bitcoin's price?