Of course, the Mercator projection is one of the reasons.
However, the line drawn through Russia is not 5900km long, but about 9000km. But since the earth is round, you can shortcut over almost the North Pole, which is only 5900km. But that looks quite different.
nitter.app/Velofisch/stat…
tinyurl.com/2ykxgc77
britannica.com/place/Russi