Because at the end of the day, "profits down to 0" also means things like "reserve capacity down to 0", "safety margins down to 0", and "any aspect of the experience that makes it less miserable than being crammed into the cargo pen down to 0".
A modest regulated profit could result in a healthier industry-- one where the least economic hiccup doesn't cause carriers to shut down with limited notice, where they can afford to not play chicken with hours-of-service laws and maintenance standards, and where people don't get promotions for trying to sell the idea of standing-room tickets.
The industry is extremely safe. Neither of the two recent fatal accidents involved safety lapses by the airlines and air travel is so safe as to be difficult to measure.
I don’t understand how higher profits would translate to a less miserable experience. Nice experiences are available now! You just have to pay for them. All regulation would do is remove the option of not paying for them. If you want to pay more for a better experience, nothing is stopping you now.
The fact that the airline that just went under was one of the most miserable, most nickel-and-diming ones out there suggests that this isn’t actually the way to compete, and the market does allow for some room at the bottom there.