Why Do Cables Affect Charging Speeds?

I had P1 Turbo with 5000mah battery. It's SC-13 could 0-100 in under a hour even with wifi enabled. The charger is broken but I keep the cable. I use a third party 2.1A charger with dual ports. The weird thing is. My G7102 and Note 3 N9000 gets charged slowly with that cable compared to the original cable of Ace 2. Ampere says Samsung cable gives more than 2 times amperage. Why is that? I don't know electronics can someone explain it to me why is that?