Why do some U.S. airports have private security, but others use TSA?

NPR reports that approximately 20 U.S. airports operate under private security contractors rather than TSA screening, a distinction that affects how passengers and cargo comply with federal aviation safety standards. The article is bylined to Bill Chappell at NPR, a major national outlet with strong editorial standards, lending credibility to the reporting, though the metadata provided does not include detailed sourcing or named officials to verify the specific '20 airports' figure or the reasoning behind this split. Independent search results corroborate that this is a recognized distinction in U.S. airport operations, though they do not provide additional detail on the rationale or performance comparison between private and TSA security models. Readers should note that the full article body is not visible in the provided metadata, limiting assessment of whether the piece explains the historical, regulatory, or operational reasons for this two-tier security system—critical context for understanding the topic.