[justsomehnguy]

Not enough KGB officers to tail them.

/s

There was multitude of reasons but the main ones were what you needed to have a good standing in the society[0] and the need to control every aspect of that society. People who would see a (even a little) better living could start asking questions. One could say that was a result of fear.

[0] the article provides one such example:

> Because of Dmitry’s active involvement in the communist youth groups, when he was 15, his school sent him to the Pioneer summer camp in Nordhausen near Erfurt in East Germany.