The seals of state/central governments are made in government presses, which is not the case for private companies. Any roadside vendor can make seals, and they may decline to manufacture government seals out of fear. Government companies follow the age-old practice of using plain paper with a seal/stamp, which is not the case with private companies. Nowadays, most letters are generated through computers, which do not even require authentication, for example, bank statements, credit card statements, etc. Frauds can be executed by unscrupulous individuals regardless of the mechanisms in place.
Regards,
Pon