I do not know if this was the rationale, but presumably the powers that be could not see any upside to civilians possessing such equipment - after all, it could be used for purposes like calling the bluff on the official narrative

('During the recent fire at the Chornobyl nuclear power plant, only trace amounts of radioactivity has been detected outside the immediate vicinity...')

or espionage ('Hmmm... I wonder why many of the freight cars coming down the track from the alleged paint factory in East Podunkskij are 100x more radioactive than those from other areas?')

We are, after all, talking about a system which restricted access to photocopiers.