I think most people are rather practical when it comes to numbers and adding two three digit numbers is generally not very practical. A cup of rice is simple and direct compared to 7800 grains of rice. How much water does it take to cook 7800 grains of rice? We use 2:1 water to rice with our cup of rice, do we use 2:1 with our grains? What is 15600 rice grains of water? Should we do the conversion through weight or volume? Things get complex fast and with little reward so most just grab a measuring cup and dump two of them filled with water in the pot, one of rice and have their curry. These simple methods of dealing with numbers scale well and avoids math, need more rice than just use a bigger scoop, still 2:1 does not matter if that scoop is an 8 ounce measuring cup or a 5 gallon pail.

The numbers themselves are a needless abstraction most of the time and the digits we are born with are all most really need.