Beyond the limp in vols, vol of vol has been marked down significantly. Nonexistent bid in $VIX calls better reflects the lack of fear despite heavy delta1 flow continuing to unwind. Suppressed vols provided mkt stability so far. Something about breeding instability I think...
There is an idea of liquidity, some kind of abstraction, but there is no real depth, only an entity, something illusory. Though flow toxicity is hidden, and you can get a quote & feel an HFT algo tightening spreads, maybe you can even sense an order book... it's simply not there.