Why are airports like Roswell and Fresno so popular for flight tests? I recently visited Roswell, NM, and was surprised at how many flight tests have been performed there.  Even the fatal Gulfstream flight test crash happened there. My research shows that a lot of flight tests happen at places like San Bernardino, Roswell, Fresno, and  Moses Lake. My research turned up only simplistic explanations for why these airports are so popular like "Boeing chose the San Bernardino facility because of three factors: hangar size, availability and weather." (Source: The Sun News)  Is that really all they consider in determining flight test locations?

I've heard that you can't do flight tests at just any airport, though I haven't been able to find any relevant legal restrictions.  The airport choice doesn't even seem to be just the obvious factors like weather, runway length, and GA availability.  (I also don't care about specialized testing that would require unusual airports like long runways or specific temperatures.) There are a few dozen low-volume long runways in the arid American West and similar regions.  Why are just a few so popular?  Are there any FAA (or EASA) restrictions on doing flight tests at any old airport?
You can do flight tests from almost any airport, but it helps if:


The weather is dry and stable,
the field is not too far from the factory,
there is a large unpopulated area nearby, and
you have support facilities available.


The support facilities were installed by the Air Force, and the other factors were already taken care of by Mother Nature in the case of places like Fresno or Roswell. Given that the distance from Los Angeles, a major aviation industry hub, to Fresno is only a bit more than 200 miles, flight testing in predictable weather and over the open terrain west of Fresno becomes very attractive. If you look at Lancaster, the next town near the vast Edwards Air Force base, the driving distance to Los Angeles is only 70 miles. This should help to explain why Edwards is today the main Air Force test base. Once you have a long runway and some experienced flight test engineers in place, other manufacturers will also converge on this location in order to make their flight testing more predictable and effective.