Why would the origin point in the PDF coordinate system is at the bottom left of the page? Why?

This must not be the case.

Ii's not defined in the PDF Standard but mostly a choice of the library.

For the reason why: Why not? XD

The bottom left is the natural origin of any coordinate system. The question is why the coordinates system from a computer has it’s origin in the top left.

@Sumafu I believe that has its origin in the starting point of the beam scan cycle for old CRT monitors.

@Sumafu Probably because developer worked on it and not a mathematician!
For PDF, I use Scryber lib in C# and don’t remember name in Java (FoP maybe ?). Both don’t need coordinates and are closer to HTML/CSS.
Wrote my own mini lib for excel generation with “flow” close to html.

@monkeyboy
@sumafu
@NoToJavascript

https://en.m.wikipedia.org/wiki/...

Has less to do with mathematics, more practical reasons....

You read from left to right, top to bottom - so top left corner is the origin point.

Most APIs I know (OpenGL, PDF, Images ...) instead do the "right" aka "mathematical" approach and use the bottom left corner as in the quadrant 1 of an coordinate system.