That's basically cause BTC was recovering at a full speed and everybody was riding that train instead of buying alts, to go worst the altcoins USD value would go slightly down but the BTC value would go heavily down since the value difference was bigger every day that passed.
In ocasions like this I prefer to ignore TA since it failed too at that time, everybody had extremely good TA's around altcoins and all of them got destroyed cause the BTC growth. Its happening exactly the same again, everybody got memory and now a big part of the market is waiting to see a similar BTC movement than the 2017 summer one, and if this happens, BTC should go really fucking fast to 20k+, in which case, BTS will fall really really really deeper than now, even in USD value. It happened in summer and it will happen again, to see some serious rebounds we would need to stay in 10-12k$ btc for at least 20 days, and it will not happen.
The real altcoin bloodbath its about to start, the BTC crazy growth will mark the start.