Yep, there's more than enough liquidity. People clearing more than $70k USD worth of ETH are usually going through OTC channels, not through exchanges like Poloniex and Coinbase. OTC fees are generally higher than exchanges, but offer the advantage of legally guaranteed finality and no chance of slippage affecting your transaction (exactly what happened with GDAX when the price of ETH briefly dropped to $0.10).

When deals are large enough, sometimes they are even executed as a set of "tranches" (large set of smaller transactions over time) so the transfer isn't easily traceable and counter-parties remain largely unknown.