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Number portability is regulated: https://www.fcc.gov/general/wireless-local-number-portabilit....

The regulation seeks to promote competition and consumer choice. An onerous verification process would undermine that goal. Security is not a consideration.

This is sort of the point with regulation. The regulator makes the rules it thinks are best according to the considerations it thinks are important at the time. If someone later shows up with different considerations, they can go to hell.