While the Soviets did not dominate, they certainly did have fairly good success, though not on par with the U.S.
I have heard many reasons for this ranging from poor facilities to poor nutrition. While these were limiting factors, they were certainly not unique to track and field athletes.
It seems that the main problems were the leadership and the lack of criticism of the leadership. Just like in the U.S. some coaches and administrators were not always appointed for the right reasons. Keep in mind that sport and politics were intimately intertwined in the Soviet Union. Goskomsport (the USSR’s national sport program) was a communist state controlled organization. Because of this, the CCCP often appointed top officials on the basis of favors or who would make the least amount of waves within the system.
Because the journals were also controlled by Goskomsport they were screened for critical remarks. Ben Tabachnik (former head of a Soviet research group for sprinters) got in a lot of trouble for criticizing certain officials for the lack of results in the sprints since Borzov won the gold in 1972. So it was not that the Soviets didn’t realize that something needed to be changed, but it was very difficult to do so within the system.
There is also the issue of whether or not all of the research was actually being put into practice. Researchers developed many beneficial exercises, but they were not always used for whatever reason.
If there is a definite answer for why the Soviets did not dominate track events, I do not know what it is. I don’t believe that the specific exercises were to blame however. I believe this was one of their strongest points, and it is likely (in my view) that other things were to blame for their lack of dominance.
There were many reasons for variable successes in the old Communist countries, not least of which was self-preservation. Often the coaches of successful programs were very secretive in order to make themselves less dispensable. An example- EG won the pole-vault in Munich- but 9 years later, after the death of the coach, couldn’t even field two jumpers to score in the USA vs GDR dual meet.