If you want the actual answer it's because you can't. There is very little voltage going through those cables, and there is no data line at all.
If you wanted to recharge your phone through a cable like that it would take about 10 years.
You can get high quality armoured recharge cables, they're not even all that expensive, you just don't get them in the box. Apple don't even give you a charger these days, so is it really all that hard to believe that they would give you the cheapest version of the cable?