The pathophysiology hasn’t been elucidated on great detail, but we do know that chronic alcohol intake reduces the expression of the thiamine transporter genes, preventing efficient absorption of thiamine from the gut into the body. I don’t believe it’s known how the transcriptional change occurs, but alcohol and it’s metabolites are quite varied in their binding and interfere with a TON of biochemical processes compared to other drugs.

https://journals.physiology.org/doi/full/10.1152/ajpgi.00132.2010