> ask yourself why the mercator projection was so popular for so long

Besause maps was developed as tools for navigation.

But if you want an idea of the relative sizes and positions of the countries of the world, you should use a globe.

Regarding colonization, I’d note that Greenland, Canada and Siberia wasn’t the greatest colonizers. The conspiracy theory about Marcator justifying colonization does not really make sense. Norway, Iceland and Greenland gets a much bigger size boost than Spain, France and UK. But Greenland was colonized, not a colonizer.

> 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