Why do they fail? An obsession to make a name for themselves above all else. For those with serious credentials then it’s wrong place wrong time.
Conversely, the successful ones I.e Easyjet, Ryanair capitalised on deregulation and shook the market up, they also created a gap for Jet2 whilst destroying the traditional charter companies like Air 2000, JMC etc etc by decimating the market forcing consolidation and the ultimate demise of Thomas Cook.
The smaller ones like Eastern, nobody really knows how these survive but it’s usually an expensive hobby for the owner(s) who make their money in other sectors and are happy to just keep throwing money at them to keep them afloat.
Barriers to entry in the airline sector are extremely high and are only getting higher as the environmental impact mitigated by increased taxes/costs, the OP alluded to the old saying, and in most cases it’s true. However, in the case of airlines like Jet2, that made a couple of people a lot of money!