Those electronic transfers are used to buy goods that already have the cost of manual distribution in their price
True, true - and the value is that it's a system that already exists and functions efficiently to serve consumers, whether or not food stamps are added to the mix, as opposed to a second system.
Besides, I'm sure OP knows this, but giving a bag of rice and beans wouldn't serve the purpose of the SNAP program. The government wants people to have their choice of products which are primarily made of corn and wheat to help keep up demand for them...