Oligopolies gain advantage via loophole mining and lobbying efforts. Lobbying efforts by the big 3 US auto makers crush small Diesel engine options. VW is forced to loophole mine (this is sometimes called cheating when another firm can pressure regulatory bodies to enforce ).
GM/Chevrolet has had methods to cheat emissions testing standards for years by forcing transmissions to skip from first to 4th gear under normal throttle conditions seen in testing. This is actually far simpler than what VW did but functionally no different. But they get a pass because V8 and jingoistic boomer Americana and all that.
All of the other car manufacturers have also reclassified most of their small cars into “light trucks” to pass CAFE ratios. In reality, they are just hatchback cars lifted into giant wheels with inefficient AWD systems added. So you end up with a small hatchback classified as a light truck and no longer possessing the efficiencies seen in a regular small sedan or hatchback. This allows GM, Ford, etc to continue selling giant gas guzzling trucks, and is directly a result of lobbying and influence buying rather than market forces. Yet VW managed to still compete within this regulatory framework, and only was nearly crushed by having to do what it took to survive. Yet, VW diesels in small cars still provided a viable and efficient alternative for people who could benefit from them. Their diesel gate motors were not that bad in terms of emissions for a diesel. They simply could not compete with the ridiculous standards lobbyists dictated to governments who approved them, so that people would have to step up to a $55k Benz or $75k pickup truck if they wanted a diesel.
Diesel is a great ICE method if you drive long stretches. VW wasn’t trying to kill you or the planet. They were trying to give you a better option than gas if you were a good candidate for it.