There are almost 20 different visa applications forms, each for unique circumstances to enter into the United States. Some are easier and more likely used than others for fast processing and requiring less background investigations.
The State Department outsources the processing of visas and in some visa classifications there are annual quotas that can be finessed by waivers and or exemptions. There are even legal cottage industry members that handle the complex legal process with enough money, they know how to skirt the process and hasten the approval process.