Part of Fitt's Law. The corners of the screen infinitely large so they are easiest to target. As you said, just "throw" your mouse. The edges of the screen are infinitely long (1 dimension) but you still need to target the X range. Still easy to target. UX designers use to study this stuff and apply it. Now they unwittingly undo all of these thoughtful experiences with their cosmetic changes.

https://en.wikipedia.org/wiki/Fitts%27s_law