That probably contributes, but that can’t be the entire story. A previous post on HN discussed the means by which the soviets excelled at identifying CIA agents

That probably contributes, but that can’t be the entire story. A previous post on HN discussed the means by which the soviets excelled at identifying CIA agents working under diplomatic cover - it turns out that American tradecraft was hardly as great as we believed - their sloppiness meant that CIA agents under diplomatic cover had unique payscales, tour lengths, working hours, socialization habits, and many other attributes that allowed their covers to be blown. If you can uncover the handlers by their sloppy tradecraft, surveilling and rolling up their assets isn’t going to be that hard - the lack of constitutionally guaranteed protections just meant that those networks could be rooted out quickly once uncovered, but it didn’t necessarily have to contribute towards their discovery.