Phenomenal answer.

The only other thing I would add, is the over dependency on large A321 aircraft by ULCC. Airbus sales guys really paint a pretty picture of that aircraft, and fleet acquisition groups swallow it whole. Unfortunately, its economics are shaded by rose colored glasses. It requires the airline to fill it up, which inadvertently narrows the markets it can operate in, it becomes financially impossible to launch into new markets, or serve underserved markets with lower foot traffic because you can't fill the aircraft and generate the traffic to sustain A321 operations. Inevitable aircraft get pushed into larger markets, and now the ULCC is competing directly with the big airline, which own or control the market. The Legacy/Major leverage their size, rewards program, basic economy fairs and upsell, while the ULCC has nothing to offer, except razor thin margins or flights losing money. The ULCC market essentially flew itself into coffin corner, flying to many A321, offering too many seats in markets, and unable to compete and open new markets or underserved markets allowing startups like Breeze and Avelo to have niche space and market room.

Finally, they did not secure aircraft/engine lease terms with sufficient protection language to protect themselves or receive compensation due to supplier/OEM issues.