It's an interesting thought, but I don't think Bitcoin's liquidity is that much of a factor when it comes to its correlation with the stock market (or rather, the stock market lows). Arguably its relatively high liquidity and 24/7 market is actually alleviating volatility somewhat, e.g. the Nikkei 225 Monday crash would probably have been less pronounced if there'd be price discovery during the weekends as well. (of course after-hours trading exists, but trading volume seems to be rather limited)

I think the far larger factor and simpler answer is that Bitcoin is still being viewed as a high-risk asset. As such it gets the boot first when managing risk.