Bitcoin is no longer crashing, the crash happened months ago, what we are seeing right now are corrections, sometimes the price goes up or down but not much of interest is happening right now, the only ones keeping an eye on the market are traders and speculators, everyone should be concentrating instead on trying to get as many bitcoins as possible.
It is not currently getting crashing out but probably OP is asking about why it has fallen from $20,000 to current price levels. First of all we all must understand that the price rally of $10k to $20k which happened in less than 30 days of November 2017, was just a bubble which got burst out in 2018. Just accept the fact of, the realistic value bitcoin may have in 2018 is around $10k. Now tell me bitcoin got crashed out ? No, a pull back from $10k to $6k is very much normal in bitcoin markets as it is always known for heavy volatility.
When $10k is the reasonable price level by the year 2018, we can expect people to book profits which is obviously taking the market to fall down unless otherwise there will be any supporting positive news is happening. Always the down market is heavily driven by FUDs and uncertainty hence new investors will opt to stay away which will lead to deeper falls.
This is the actual things happening in bitcoin markets hence it is not crashing out but still trading at reasonable levels from what momentum it got from the year 2017. Probably levels like $8000 to $9500 (in down market side) or $10500 to $12500 (in up market conditions) must be the right things by August 2018 but we are into $6500 levels which may be considered as crash but actually it is not. It is just a heavy sell-off state due to FUDs and profit-booking by whales.