The trials are looking for a drug that does that without lifestyle changes.
There are tons of studies that show that better lifestyle helps, it's just most people can't do it. Not eating trans fats is one small change that will help, that is also easily done.
New insights into the possibility of plaque regression have been elicited by the ASTEROID, REVERSAL, and SATURN studies that utilized intensive statin therapy and demonstrated plaque regression in majority of study patients. However, these trials showed less than 10% regression in overall plaque volume only, which may not explain CV event reduction.
You've changed your claim. First you said a healthy diet will reduce plaque volume, now you say it just helps reduce heart attack rates.
Even the studies you cited only show minimal plaque volume reduction (so small it's questionable if it helps at all) and only with intensive pharmacological therapy.
There are tons of studies that show that better lifestyle helps, it's just most people can't do it. Not eating trans fats is one small change that will help, that is also easily done.