Here is the top 3 reason:
1) https://cryptotown.io/news/bitcoins-surging-dominance-is-this-time-really-different-coindesk/index.html
2) https://cryptotown.io/news/bitcoin-drops-to-10000-in-recent-downtrend-cointelegraph/index.html
3) https://cryptotown.io/news/bitcoin-drops-to-10k-in-worst-daily-loss-in-a-month-coindesk/index.html
It's not a new news that bitcoin's price is falling since last 2 days and today it has gone below 10k. Speculators will speculate anything but tell me, is this the first time you are seeing this kind of trend in 2019?? Bitcoin is continuously going beyond 11.5k and coming down to 9k. We have seen such trends quite a few times in this year, especially since last 3 months. See the chart below and look at the highlighted area of head and shoulder's pattern.
I firmly believe, that another similar type of trend is in the making and it will continue for some more time. However, I only agree with only one point from the article of Coindesk as quote below,
Increasing dominance can lead to utter massacre and there will be no area of recovery if anything wrong happens! Lets just wait and watch but I believe, bitcoin below 9k is still a gift!