I think much the same as I think about all the "this means that about everybody"-theories -- but, as this is polite company, I won't actually voice it.
Different things bring different people to both aspects of the lifestyle, and trying to pigeonhole everyone into one reason is typical of someone who doesn't understand human complexities -- or someone who wants their article to be well-received so they'll get another assignment from the magazine, because over-simplifying a complex issue will please the majority of readers.
I've met submissives (and dominants) who fall everywhere on the insecurity-spectrum, but my overall impression has always been that the majority are more secure with themselves than the average person.