> Besause maps was developed as tools for navigation.

It's not perfect for navigation either, especially over long distance if you want to navigate from Europe to the US, going in straight line over a Mercator projection is going to make your trip much longer than it ought to be. So while it makes sense for smaller-scale maps because the angles are preserved, it's totally pointless for a world map.

As an example compare this to the straigh line between Edinburgh and Miami in mercator projection: https://www.wolframalpha.com/input?i=edinburgh+miami