This is a good point, but Amazon tacks on even more fees if you want to fulfill those orders outside of Amazon. We used to sell small electronics on Amazon and other channels which used to cost $2.60 to ship USPS.

We signed up for FBA and they charged $5.95 to fulfill each order. Even if picking and packing costs $1-$2, you still make more profit shipping it yourself. We used to have 3 workers fulfill 150 orders a day from our warehouse which equals $0.80 to "pick and pack" and can be sent to any channel.