> it was by the layers upon layers of interconnected unregulated derivatives valued at a few orders of magnitude above the underlying subprime mortgages given to anyone with a pulse

It was interconnected derivatives and structured products linked to banks that caused a liquidity crisis in the former to cause a crisis of confidence in the latter.

Meanwhile: "In the letter, Morgan Stanley said the fund wasn’t designed to offer full liquidity because of the nature of its investments, and that credit fundamentals across the underlying portfolio have been broadly stable. The bank's shares fell 2% in premarket trading Thursday" [1].

[1] https://www.wsj.com/livecoverage/stock-market-today-dow-sp-5...

That was the structural problem. Definitely bad. A weak economy propped up by some 'fake' money.

Oil was more of the outside force that put a shock to that weak system.