I think this was just a temporary one because I can see from coin marketcap that majority of them are green again,  although this is not yet the time for altcoins and many who understand the market will see that, it’s best to convert altcoins to BTC now which has usually been the practice in the past once bitcoin start running on bull, and once they have taken enough profit they want from the Bitcoin bull market, they reinvest in these altcoins again.

So, the red you see might not necessarily mean that the altcoins market was fully abandoned or dumped, it’s just a strategy many people learnt to have both in their favor.