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, its 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, its just a strategy many people learnt to have both in their favor.
Holding less altcoin and more Bitcoin was indeed the strategy played by artitraged cryptoneir whenever the crypto market poses the strength of bullish market which is why Bitcoin dominance surpasses altcoin. Despite that we all have different point of view and understanding about the market.
indeed for this year most people are holding bitcoin from altcoins in order to get big profits later, because this year bitcoin will definitely experience a good price increase and will promise also