OK, it's clear that mouse cursor has it's shape by historical reasons. But since 1995, didn't anybody make usable straight or reflected mouse cursor? MS Word uses reflected mouse cursor sometimes. But it's really weird that even searching for straight cursor theme just answers why the cursor is not straight and doesn't provide any usable themes.
EDIT: I'm looking for a style or theme which does use straight or reflected mouse cursor, because sometimes I use left-handed mouse, and it's not convenient to keep it's shape as right-handed version.