Sorry to sound stupid but what is the point of an emissions defeat device?
These are comparatively cheap ways around that.
Edit: people generally don't do things for the "sole purpose of polluting more" it's often functional. Many diesel drivers don't like others who roll coal as the image is bad in general - heavy equipment will often produce black smoke because the engine is being worked for a purpose and it's literally just being given fuel.
If you spent $100k on a truck, and you could spend $2k more to 'delete' some emissions equipment to prevent $10k+ worth of repairs in the future, would you do it?
At least cars have cabin air filters. I get to suck it straight in unfiltered.
At least cars have smog equipment to reduce the emissions. Motorcycles mostly don't.
I remember turning it off in Europe because trying to start from a dead stop with the engine off in a stick shift is a whole new world of fun I didn’t need.
Otherwise, you do it to make your street car faster (and maybe also pollute more), or worse, just generate a bunch of diesel soot to annoy other people with.
Many states and localities have "visible emissions" rules, where even if your vehicle doesn't have to pass emissions tests, you can still get pulled and cited for actual smoke. I've never been pulled for it (smoke means you're wasting fuel) so I don't know if it's an inconsequential fine or just not enforced generally.