Van’s is doing what they claim to do. They aren’t about making the best planes. They are about making the best kits. Their customer base was earned, and is now a big advantage;however, who has tried to outdo them and failed merely because of their market advantage? Seems to me that builder assist programs from other makers still don’t lead to enough finished planes to compete.
Another reason they can sell so many is that the certified aircraft makers are not moving the bar. There was a time the certified manufacturers were selling tens of thousands a year. Cessna has instead decided that it will continue to sell the same old planes. There’s your problem. When their competitors actually make better training aircraft, they still end up losing because the industry has made the 172 a standard and the government keeps letting them build the same ones without even having to put in modern safety upgrades. In fact, if they made the stall characteristics safer, the schools and airlines would likely complain!
At any rate, one reason kit planes sell so well is cost. Unfortunately, it’s often less about the journey than the cost. And why is the cost less in spite of economics telling us the specialized manufacturers should be more efficient and cheaper? Liability, the FAA, and of course labor taxes and mandates which it seems the home of the free is over run with.