Why are there different systems of measurement?

Question

You know, we have metric system, English system and the SI Units. Sure we all agree on the SI units but why do these systems exist in the first place?

Answer 1

During history, each countrey had its system

In modern times after nearly1800, people wanted to have systems for small quantity called CGS centimeter, gramms , second, or large quantities industry MTS , meter, metric tons, second

Now, there is an agreement use only system called MKSA universally adopted

Answer 2

We still have stone-age measures in the USA because retailers want to keep consumers confused about how much they're getting for their money. The old-English units were developed by merchants thousands of years ago. Each local area had its own system because there wasn't much trade across borders. They couldn't have created a sensible system even if they wanted to because science hadn't been invented yet. Besides, kings and dukes and warlords were extremely vane; they insisted that their own body parts should be the standard of measure.