All you have to do is look at Coin Market Cap or Coingecko at the little charts at the left side and you will notice that most alts do follow BTC.
Initially the altcoins also went up, along with Bitcoin. But now the trend has reversed. Bitcoin prices are stable, while many of the altcoins are crashing. For example, XRP (Ripple) has lost more than half of its value during the last few days, and many of the alts were also affected by its drop. But Bitcoin prices seems to be stable and it was not influenced by the SEC lawsuit against Ripple.