I mean I wouldn't do business with them, I think the supplements industry is infrastructure for grifters, quacks, and pyramid schemes to fleece the desperate, but what's the problem for Visa? Is it a brand safety thing? My presumption would be that payment processors are amoral and have no problem processing payments for Consolidated Baby Kickers if it were legal to do so, is that a misconception?
"Not as advertised" chargebacks. That industry is also full of subscription scams (e.g. someone thinks they're ordering a supplement for $5.99, but they're actually getting signed up for $39.99/month...).