Switching the gas to nitrogen would result in a relatively peaceful passing by comparison. Shame.

Handling nitrogen is more dangerous than CO2 for the same reason it is more humane for the animals; you don’t notice you’re being asphyxiated. Not that it is impossible or even particularly difficult to handle nitrogen safely, but it would incur a cost (training, equipment, ...), and inevitably result in accidents when these costs are skimped on.

Unless legislation changes, it's simply better business to let the animals suffer.

You dont need pure no2 for pigs. You can mix in a substance that makes it stink to high heavens so it is safer.

Alas the rest is true re costs being higher and legislation changes being required to force an industry shift.