Why did Gabriel Mouton devised the metric system?

Answer 1

First, he didn't invent the metric system as we know it today, but he did do a couple things that advanced it. Thus Gabriel Mouton is considered the "father" of the metric system.

Why did he do it? One can only guess - I presume because he observed a way to do things better, cheaper, and faster. As Mallory said, "Because it's there."

Like our modern metric system, Mouton proposed a decimal based system. So converting between meters and centimeters would be much simpler that converting, for example, inches to feet. People really gravitate to this once they understand it much like people gravitate to decimals and not fractions.

Next was uniformity. There were zillions of standards for weight, length, and time. Mouton proposed a uniform standard.

However his base unit of length was, what we now call, a nautical mile. That is, one minute of an arc along the equator. The metric system eventually adopted that there are 10,000 km from the equator to the north pole. While this was later refined, it remains a close approximation.

This is the short and sweet answer, however like many things there were a lot of details omitted.