Since all cryptocurrencies are linked to Bitcoin, most of the other cryptocurrencies fall following Bitcoin as the price of Bitcoin declines, which of course is a big drop. As for why it's a good time to invest in cryptocurrencies, you can get more coins at a lower cost because all currencies are falling.
this is true since it happens every time bitcoin either drops or rises.
but also altcoins would have dropped anyways even if it wasn't because of bitcoin because they were pumped a lot in the past couple of months and the "wise money" which got in before the pump and initiated the pump itself had to exit to make profit.
and i also disagree with saying it is "a good time to invest in altcoins" because most of them are dead because of this dump and won't recover for a long time. and others may have some dead cat bounces and then continue dropping more so it becomes riskier to invest if you are not a day trader.
I agree. However, even if you would think that the market might be in grave danger, I would say that it is still part of the normal market movements, plus cryptocurrencies always have this feature of being unpredictable. I think the better move here than being worried is taking the chance to enlarge your collection of coins, which would become big once the coins regain their strength and increase their values again. While it is true that many coins might not comeback from this grave situation, I think that it is still a good time to invest, if you just choose the better coins that would survive and be able to again increase in the future.