It's all to do with cheap and nasty design and the watered down EMC Immunity standards.
Rather than meet an appropriate level of RF Immunity, the Manufactures/Importers lobbied the FCC to permit Lax standards and instead rely on a FCC Part 15 Compliance sticker which reads "...this device must accept any interference received, including interference that may cause undesired operation".
Rather than meet an appropriate level of RF Immunity, the Manufactures/Importers lobbied the FCC to permit Lax standards and instead rely on a FCC Part 15 Compliance sticker which reads "...this device must accept any interference received, including interference that may cause undesired operation".