Because thiosulphate is safe compared to acids and cyanide. Creates h2s and sulphur dioxide gas. Lot easier to deal with than nitric oxide and chlorine gas. And it works. Been electrowinning my silver today and it's gained about 8 grams already.What about doing things with leaches that are used in the industry?
There usually are reasons for a technique to not be used, especially if they are cheap.
If I remember correctly, this was brought up early in this thread.