It's not that they are not liable, it's just not worth pursuing. Yep, you need to understand how pharmacy works. There's rules in the CSA 1970 that have additional liability for distribution, which this is what the pharmacy's are being accused of. The problem is, Walgreens, CVS, and others suppressed reports. I know specifically in Walgreens case as I was disciplined for such reports in my early career (and now have a high six digit as lawsuit avoidance compensation and my old RxS doesn't have a license anymore).
Do the right thing when it comes to these matters. It pays off in the end. This very board got me quite a bit of money with some student bragging about what amounted to Medicare fraud with educational funds here. Tipped off the CMS, got my 25% bounty (which honestly is more than the Civil Service would pay me over a career), and that school had to pay an extreme settlement.