Because between the $2 cheap charging cable and the $40 do-all cable there are many variations; the $2 cheap cable can be limited to USB2 speeds (480 Mbps) and

Because between the $2 cheap charging cable and the $40 do-all cable there are many variations; the $2 cheap cable can be limited to USB2 speeds (480 Mbps) and 3 Amp charging, but when you go for better you can pick and combine more charging current (5A), better data speed (5 Gbps or 10 Gbps) or both. Depending on what you want, current requires thicker wires but data speed requires better electrical quality, putting everything together is more expensive. Still, you can find good cables at $15, but not in the Apple store or on Amazon, their costs and margins make the $10 cable from China retail for over $25, even $40.