The reason for the legal requirements of flying public transport are to put in place the checks and balances that assure to the greatest degree posable that an accident won’t happen and this costs a considerable amount of money.
The reason for illegal public transport is to do things on the cheap by ignoring the rules put in place for safety.
This case illustrates perfectly the result of such practices and it matters not the particular holes in the Swiss cheese that aligned to create the inevitable result.