[paul.fr]

they do on my maps, but do they actually?

[another_someone]

Rivers flow down from mountains, so the direction they flow depends on where the mountains are, which depends on the plate tectonics in the region when the mountains were created.

Around here, the major river is the Thames, which is East-West (although its tributaries are another matter).

In Italy, which is a country that is oriented North-South, and has a mountain range down the middle, you'd be hard put to find a river in the central region of the country that flows north-south (in the north of the country, you would have rivers flowing south from the Alps, but not in the central region).