Did they draw the government's attention because they were connecting to banned websites or because they were running a high-profile news outlet?
It's seems unlikely to me that the Iranian government would be able to prosecute even a small fraction of instances of the former, whereas there's only a small number of high-profile news outlets at any given time.
Due process is not really a thing in Iran. If the Government wants you in prison, they will throw you in on flimsy pretexts. Which is why journalists need to be extra careful: they don’t just need to hide their activities but need to hide any trace or hints of participating in those activities. Outspoken people will be monitored closely, and even an attempt to access signal (say) could be used by the Government to imprison the user.
