> 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.