Here's my theory:
1. Algo trading now is 80%+ of all trading
2. JPM, Goldman Sachs and a few other players now control > 60% of all algo trading systems
3. Pinning because of short term options is also > 90% of the influence on the underlying... the tail is now wagging the dog.
All these factors which basically represent SEC sanctioned market cartel control make it impossible to have crashes or any sort of herd panic in the markets. Consolidation of the means of trading into a few hands which are a de facto such a cartel by any definition make it impossible to have a repeat of 1929, 1987 or 2008.
The same rules apply to crypto where 80% of the "mining" is controlled by a small clique of server farms which also were consolidated under the control of a select few companies.