Probably because Amazon is at this point well known for shipping counterfit products. That's dangerous when it concerns phone chargers. It's downright negligent for supplements if you ask me.
Suppliment maker/seller here. I agree, its a surprisingly shady business. However many store/drogery brands too have their flaws. Big brand suppliments often contain cheaper chemical alternatives, while smaller brands sometimes really care about the actual source product.
Its hard honestly. Thats why i am making my own.