I look at it this way, when you 1099 yourself you represent yourself as a mini business to your employer. You're responsible for the overhead and risk of that business. That additional cost and risk could easily could represent 2x what a standard salary rate would be for the same position.
Keep in mind contractors can't be expected to be employed consistently, so they have to bake in additional income to tie them over between jobs, or handle the possibility of being unexpectedly terminated. They're trading additional income for added risk and uncertainty.