Maybe because most of us are not law breaking criminals willing to risk everything on the off chance our birds start an epidemic.....
You must be someone that does not believe the rules apply to him...thankfully you are the minority.
Well, that was rather snarky. I was not going to offer anything else to the OP but since you have so swiftly insulted me, let me continue a bit, then I'm done. I am breaking no rules, contrary to your accusation. To sell eggs and chicks off the farm, I do not have to register with any government agency. If you show or mail birds and eggs all across the country, you must belong to the government program. I said that, in case you missed it. I do neither.
And actually, I am not in the minority. I bet the majority of folks selling hatching eggs and shipping birds over state lines here on BYC are not NPIP nor do they have a vet's certificate of health. Most are just casual backyard flock keepers trying to sell extras to make up some feed cost.
Again, NPIP was not created for backyard flocks and it was never intended for them. It is an ineffectual program for preventing disease as it only tests for the rarely seen P/T and sometimes, depending on the state, AI, and it relies on the honor system from its members. It lends a false sense of security if people believe it to be more than it is. There is no way that registering your flock to be tested for two almost eradicated diseases yearly can protect your flock. Are they going to come put a dome over your house? I think not. They will, however, know where to come kill your flock if you are in the kill zone during a major outbreak among commercial flocks, which I truly believe is part of the point of pushing for this by the USDA, but I digress. The false sense of security of an NPIP flock is all I hoped to impart to the OP, if she was going to buy and sell to other NPIP people.
To illustrate the inadequacy of the NPIP program, it was an NPIP breeder in Washington State responsible for the spread of ILT, a particularly nasty and reportable disease that will necessitate the government coming out to kill every bird on your property if you have one test positive for it.
I know of a case in Indiana of one NPIP breeder selling an ILT carrier rooster to another unsuspecting NPIP breeder, who properly quarantined him for literally months. With no symptoms showing in him, she put him with her breeding hens and they all became ill. She called out her tester, who found ILT, which meant the rooster had to have been infected and recovered, or been vaccinated with the live vaccine. The government folks took every single bird on her property, even coops that were far away from the affected one, and put them all in a gas chamber, one by one, then gave her a list of rules telling her what she could and could not do from there on out. Again, an honor system fail and one reason NPIP is not what it is cracked up to be.
When people seem so happy and positive about being NPIP, I want them going in with open eyes. That was the purpose of my original, and this, post. Rose colored glasses have no place in chicken-keeping.