They were not utterly oblivious to the outside world and accepting of the government and party line from 1917 to 1990. The last one already sounds completely implausible it should give you pause - that would make generations of Soviet people utter naifs. They weren't.
Firstly, the soviet Union was made up of a number of separate countries (as the original article notes things were quite different in Russia, Lithuania and East Germany. While all lead by communist parties, all operated in fear of Russian occupation (as happened in Hungary in 1956 and czechoslovakia in 1968).
Soviet block countries were dependent on Russia for aid, and military support. In the late 80's Russia was unwilling, and unable, to spend the necessary money to cover all the needs, so states prioritised food (on the basis that starving people are seldom compliment). Necessary maintaince of (for example) the border fence between Hungary and Austria is not paid for (by Russia) leading to the first domino falling and a route being opened to the west.
In Poland and Berlin popular movements progress quickly, and in both cases Gorbachev refuses to use the Russian military to prop up those govts.
These are but the broadest strokes though - obviously there are a lot of moving parts, and a lot of different populations in play. But money is at the root of it all, and Warsaw pact countries needed money to import food from the west.
Your newer stuff isn't much better (Hungary didn't let East Germans into Austria because the fence was under-maintained) but that's probably past the point at which should wrap this up.
It becomes harder to convince people of your position while they are starving. So yeah people stopped believing.
But there's a Long time from 1917 to 1990. And for the bulk of that time people believed enough for the status quo to be maintained.
And plenty of people in Western societies belive adds, and the evidence for this is that companies and parties keep making them...