The replication crisis definitely leaves a lot of room for questioning. However, even if all the studies we have were properly replicated we still wouldn't understand addiction perfectly. We still have a lot to learn, just look at how vague definitions of addiction are still http://www.dsm5.org/documents/substance%20use%20disorder%20f... But both addiction and learning involve the brain's dopamine circuitry; ironically when responding to your point I can't read the relevant articles I found because they are behind paywalls. This article has some interesting commentary but the sources are paywalled: https://www.thieme-connect.com/products/ejournals/html/10.10... Most likely there is a connection, but anyone who claims to understand it entirely at this point is overconfident.