[badRNG]

I think that's just because those games are written poorly and don't account for the differences in moving diagonally. If you are moving on a grid, moving forward one tile moves you the length of a tile. Moving diagonally one tile moves you sqrt(2) ~1.4 tile lengths.

[Akronymus]

More often it is because both inputs apply some speed. Like in doom.

https://doom.fandom.com/wiki/Straferunning