The most common map in western schools is a variation on Mercantor (the axis of the cylinder is different), it has the added feature that the "Land Hemisphere" (where most of the land and people are) is "magnified", so you can fit in more detail. Sure there is less detail in the "Water Hemisphere" but it is 90+% water. Water doesn't really have any details of interest to someone reading a map.
The notion that it was drawn/chosen for political/propaganda purposes is "historical revisionism" from people with an axe to grind. They, not Mercantor are the ones engaging in (not so subtle) political propaganda.