The fake SD card problem is so bad that Amazon got an exclusive product (Samsung EVO Select) that only they can sell. Rather than solve the counterfeiting problem, they just make money off it.
This is also the strategy behind AmazonBasics. It's the only brand that is exclusively sold by Amazon. Amazon is basically destroy the reputation of other brands by letting sketchy and fraudulent sellers on their platform do as they please. There are a lot of people who exclusively buy on Amazon so over time they will only trust AmazonBasics products.