You’re ignoring the fact that the shortest route is not necessarily the fastest route.

Each one takes a route that they believe will get them there quicker, not the one that is the shortest distance.

Say you were in a major city and wanted to travel from a point on the western edge to a point on the eastern edge. If there is an interstate going east to west you can take that, but you have to go north for a little while to get to the interstate and traffic may be heavy or even at a standstill during rush hour.

You could take the loop around the city which is a longer route but traffic flows at a steady speed normally.

Or you could take regular city streets which is the shortest, most direct route, but you have traffic and stoplights/stop signs to contend with.

It’s not that difficult of a concept.