These studies are meaningless, as they cannot distinguish between the effects of the drug and the effects of the illegality of the drug: constant survival stress, negative outlook on self imposed by others, social exclusion, paranoia.
Survival stress, as in PTSD, causes cortical thinning, and explains everything in the scenario without the need to arbitrarily assign blame to methamphetamine.
Survival stress also impacts liver function leading to poor lipid metabolism which in turn can impact cholesterol absorption and lead to cortical thinning. Which is also an effect that we see from methamphetamine use in various animal models, which by it's nature of being controlled trail seems to exclude the stress factor.
https://pubmed.ncbi.nlm.nih.gov/28689763/
I would agree with you in general, but there are situations where prescribed methamphetamines also lead to cortical thinning when not used as recreationally. This seems to suggest that stress may not be the entire player here https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3870784/
If you would like to read more about PTSD findings as it relates to stress and liver function, I would be happy to expound upon the way that corticosteroids impact gut bacteria that directly affect FXR metabolism and bile acids and further lead to cortical thinning. https://academic.oup.com/cercor/article/30/2/575/5521088