According to CNBC, federal prosecutors had launched a criminal probe into the cryptocurrencies earlier this year based on suspicions that their price was being manipulated. I think it might be the main reason behind the price of bitcoin dropping to around $4000, but I also wonder whether it could be that authorities are afraid that Bitcoin and other cryptocurrencies are taking over the financial system since they're now so popular.
There definitely could be concerns with that which led to prices plummeting. There may also be reasons behind this dump regarding the hard fork of other cryptos, they are all factors.
But honestly, if these news came out in a bullish sentimented environment, I really doubt that prices would be affected this much. Only in a bear market do these news stick around and result in a panic dump, because weak hands who are merely speculating on the market to make a quick buck don't have the fear of missing out to buy into bitcoin anymore, like in a bull market. The cycles of the BTC market which has been shown countless times is the ultimate reason behind all these price dips imo.
TBH, a price recovery seems very unlikely this year, but could happen in the next year after prices bottom out at $3-4k and move sideways a bit. Shouldn't be concerned at all though if you're holding for the long run, which I think most people here are doing. Short term dumps like these have absolutely no impact on how bitcoin adoption (both institutional and individual) and usage will go in the long term.