Why do they drive on the wrong side of the road in other countries?

Answer from an Englishman’s point of view: It could also be argued that you are in fact the one driving on the wrong side of the road! Lol 

Driving on the left-hand side of the road is a convention and custom that dates back to Roman times. It is thought that the switch to driving on the right-hand side of a road took place in the US in the 19th century and this was thought to be because wagons were starting to be pulled by several pairs of horses. This meant a whip had to be used by the driver to control the horses. As drivers more often than not were right-handed and this led to them being seated on the left-hand side of the wagon, so in that case it made more sense to drive on the right-hand side of the road.

Researchers believe that in the United States during the rise of freight wagons drivers sat on the left rear horse in order to control the team of animals with their right hand. Another influence was Henry Ford’s Model T which had the steering wheel on the left making it necessary to drive on the right.

Driving on the left is also influenced by an ancient Roman practice where chariot riders stayed on the left so that they could hold their weapons with their right hand. The British government actually enacted the General Highways Act in 1773 which made everyone drive on the left.