Why aren't there more replications? Maybe negative results aren't getting published.
Are there political difficulties in getting funding to attempt a replication? Political difficulties in publishing a confirmation (positive result)?
Is it a particularly difficult experiment to perform? Perhaps needing to obtain and handle a controlled substance.
I suspect there are (or will be) some positive and some negative results in replications. What determines the outcome? Are some rat stimuli more effective than others at preventing or breaking addiction? What neurological mechanisms are involved in the rat that cause the positive and negative results?
For which drugs is Rat Park effective for breaking addiction? What dosages of the drugs, i.e., how addicted? Which animals beyond just lab rats?
I suspect experimenter bias has a strong effect on the outcome.