Because it doesn't need to. Like standard arithmetic, where 2x + 3x = 5x, or where 2*5 + 7*5 = 9*5, the same holds true for elliptic curve multiplication.

Let's say you want to multiply the generator point by 20. You do not need to do G+G+G+G+....+G 20 times. Instead, you can do the following:


So, instead of doing 20 calculations, you only have to do 5.