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Never knew that and millions are so.

Why?

Because it is not used just for marine navigation. It is mostly used for everything related to maps and apps with maps.

Apps with maps use a specific and different Mercator projection which produces a nice quadtree for dynamically loading data. This is possible with other projections too, but reprojection and training users to expect a different looking map is expensive.

Almost nobody plots courses of constant bearing on a map. Almost nobody uses a map to measure area either.

99% of the use cases for maps these days are for local navigation where artifacts are minor. The differences in map projection are basically irrelevant to users in these cases.

Measuring area is a different use case to looking at the world map to get a sense of relative sizes - of continents, countries, regions, etc.

This in turns influences how you think about history, population density, travel times, etc.

But what if I'm looking at a world map to get a sense of where different cities fall on different latitude lines to gauge their climate?

Sure that’s a valid use case, 100%.

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