Wasn't that primarily because of sea trade and the mercator projection being very useful for that because you can draw a straight line on it and then set a straight course?
As such, while the Mercator projection makes total sense for a map of northern Europe or the Caribbean, it makes absolutely no sense as a map of the entire world.
Keep in mind: that's 500 years ago, not 50 years ago. There's no question that we have better tools today but the question was why the mercator projection was so successful it became the default. I think "it was super useful at the time because it made navigation easy, reliable, and available to everyone, at any any weather" is a much more compelling explanation than "the would-be colonizers spread it because their home-countries were enlarged and they liked that and used it to oppress the equatorial countries".
With a compass, a sextant, a clock, and geometric calculations to get the intermediate points you'll then use a straight course to rally these point. The Mercator projection just inverse the order of the calculations (going from the intermediate points to course is straightforward as you just go in straight line over the Mercator projection), but deriving the said points requires calculations. If you have a globe, it's the other way around.
> is a much more compelling explanation than "the would-be colonizers spread it because their home-countries were enlarged and they liked that and used it to oppress the equatorial countries".
This is a strawman though, nobody serious would claim it has been designed for that reason. The fact is that it distorted the view of peoples in a way that aligned situ colonists propaganda at home. But those claims aren't at all equivalent.
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.
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
Growing up, I did not see Mercator at all often.
However, ask yourself why the mercator projection was so popular for so long, and why resistance to other projections took so long to counter.
Maps are inherently political and about power. The lines drawn on a map indicate the concrete physical extent of abstract non-physical forces such as power, authority, and jurisdiction of law.
When groups of people went about the World for centuries (arguably millennia), stealing, torturing, kidnapping, enslaving, raping and murdering people to create new lines on maps of their authority and law, it's fair to say where those lines are drawn is important, and when those same people decide to teach these events in a very sanitised way using maps that make their own countries look far bigger than they are, it's reasonable to ask what is going on.
But we can put that aside for the snowflakes who get upset about discussion of historical events related to European and American empire building (and I say this as a white, middle-aged, British man).
In plain terms: it's sometimes useful to have an accurately sized map if you want to compare by eye the size of say the Falklands (or Malvinas, if you prefer), with Malta or Jamaica, and not get a false sense of relative size just because of how somebody decided to draw the map without caring about accurate sizing. This is useful in a wide range of educational settings relating to geography (a physical, non-political version is available for download), history, politics (versions with Palestine and Israel labelled or not labelled are available), and even economics.
It's just a fact that maps that are accurate to land-mass size like this are more useful for some purposes than those that aren't, and doing so for a large ball onto a 2D surface is hard, and a worthwhile pursuit for lots of end use cases, for reasons that are well documented in a variety of forms to suit your taste if you're curious.
The "kinds of people to complain about" the mercator projection therefore can be people who just want a more accurately sized map. What's your problem with them? Why are you so against them wanting another map projection? They aren't taking your preferred inaccurately sized map away, they're just creating a new one fit for their purposes, and you're the one complaining about it. As such, I actually think you're the one who needs to explain your thinking here. It's your thinking that I would argue is bizarre.
Perhaps you also missed the fact that different meridian options are available well away from the Greenwich meridian, and there's even a "South to the top" projection available. Perhaps you think those people who would appreciate such a map for purposes you can't imagine, aren't entitled to it, even though them having that costs you exactly nothing? It's an odd notion, far odder than the notion of wanting such things for all sorts of reasons.