If people are not allowed to go abroad at all for 50+ years, they'll naturally flock in bigger numbers once borders are open.
To be fair, there's still a huge gap between post-ussr and western countries. But we're catching up. It takes time to fix what 50 years in ussr did. Some people want money & stuff fast, they go abroad. Other people prefer to work on rebuilding their country and/or see more business opportunities in developing market.
By the way, it's not only ex-ussrs emigrating. I heard more and more Spaniards and Greeks come to Norway to earn more :)
USSR times factories were ineffective as hell. They went under simply because they couldn't stay afloat. Outdated technologies, R&D focused on specific parts of weapons, ineffective management, shitty environmental policies... USSR times factories were a complete disaster. All of that closed years before EU. And thanks god they closed. Now I can swim in a lake next to my hometown without worrying about allergies. You know how we could tell what colour carpets the factory is making that day? By looking at a lake next to it :)
