Dorna have actively promoted British riders (there used to be a lot of complaints about the riders brought in). I have no doubt that Ezpeleta had a say in keeping Hayden at Ducati. Dorna have been very helpful towards Yonny Hernandez, because they really want a South American in the championship. Teams have been told (especially in Moto2, but also in MotoGP) that they needn't bother asking Dorna for money if they sign a Spanish or Italian rider.
Why are there so many Spanish riders in the championship? Because the Spanish federation put a program in place to bring riders on from a very young age. Dorna have leapt on that program and used it to feed non-Spanish riders through the system, and if you look at the Red Bull Rookies, there are a couple of fast Germans, a fast Dutch kid and a Czech rider who is currently being tipped as the next Rossi. The Italian Federation, after years of neglect, is starting to build a program, and we are seeing the effects with Fenati and Antonelli. Even the Dutch Federation now has a full program in place, the NSF100 Cup as a step up from minibikes, then the YZF125 cup as a cheap full-size class, followed by the Moriwaki cup for more serious riders. There is a full-time national roadracing coach (Barry Veneman), who spends time with all of the Dutch riders racing at the international level, with special attention to young riders. Expect to see Dutch riders coming through in the next 5 years (and things have been awful for the past 20).
The problem is for the Australians and Americans. Neither of those two countries have a plan, a system for taking young riders and coaching them all the way through to the Grand Prix level. American entries to the Red Bull Rookies have come and then gone back to the US, because it's cheaper to race there, and they don't have to live in Europe. Australians, too, come to Europe and race. Ironically (or not, perhaps) Jack Miller has done much better than Arthur Sissis, despite the fact that Sissis has Red Bull backing as a former RB Rookie. Miller came with his parents and raced wherever he could (sound familiar?).
Don't blame Dorna for the failings of your national federation.