I recently realized that when people talk about bicycle gear ratios, it's calculated as number of teeth on the (front) chainring divided by the number of teeth on the (rear) sprocket/cog.
This made me a bit confused, because I was thinking that gear ratios are usually the opposite - driven gear/sprocket/pulley divided by the driver (e.g. motor). When talking about motorcycle final drive, the formula is rear/front sprocket teeth. When reading motorcycle/car specs, the lowest gears - 1st gear and reverse - have the highest numbers.
I tried to find why it's the opposite with bicycles, but so far couldn't...
Can someone shed some light on this topic? How this came to be historically?