* The realization that BTC doesn't scale well and might not be suitable as payment system
* Governments cracking down on BTC
* Big banks in the last few days again declared BTC to be worthless (Goldman Sachs + Deutsche bank)
* Fear of tether manipulation which might crash the market big time if it turns out to be true
^^ This
This is the most rational view of bitcoin I have seen posted on this forum in a while. These are the big problems/threats to bitcoin, and they are why the price is likely to continue declining.