Most of the people invested into alts during the highs are people margin trading their bitcoin and buying into alts. When bitcoin starts to drop, everyone must sell their alt coins to put back into bitcoin so that they don't get margin called. At the same time people are taking their money out of Bitcoin and into fiat or fiat-pegged assets. Alt coins almost always drop to a certain point because all that are left are the long term investors. This is why I think BTC and alts rise and fall simultaneously.
Or maybe because Trump and Kim Jong will be having a meeting and everyone is taking their money out of cryptos and into ammunition stocks? lol
That is why I have said that never buy with borrowed money and then there is no margin call...
use your spare money is the word but many dont heed to it that is why there is always panick sell when bitcoin drops. but am so holding