Is it because of the large number of altcoins?
Nope! Altcoins proliferation is not the main cause of Bitcoin price meltdown. This is quite normal most especially if there are lots of uncertainties in the market. As you notice even the worlds stock market right now show bearish movement. Rapid downward of price of BTC is purely cause by demand and supply of the cryptocurrency. As of the moment, we seen BTC is not performing well due to many unfavourable news. All we can do today is not to panic and wait to become normal. Right now is the best time to cost average the portfolio.