Deciding which side of the road to drive on is a kind of coordination game. In some countries, people drive on the right side of the road, and in other countries (notably the United Kingdom and some of its former colonies), they drive on the left.
These customs developed hundreds of years ago. If there were a single world standard, car companies could save some money by not having to produce both left and right types and cars would be a little bit cheaper.
Why do you think it is that these customs persist?
In other words, what keeps the world "locked in" to two separate kinds of cars?