Well it’s because you’re projecting on a plane. It’s kind of the reverse of the parallax effect.
It’s perfect for representing lines because you’re just inverting lines. That’s why your raycaster must use perpendicular increments instead of angles - you’re going to output on a plane as well.
CCD don’t have issues because they’re planar as well. If you reverse a plane, you get a plane.
As for the eyes, let’s not forget they’re spherical (kind of) instead of a plane, so they effectively see the world in their angular version, aka the fisheye effect. As jonne explained, our brain actually does the cos formula and stuff to correct it so we can see straight lines! Fortunately you don’t have to deal with this.
Anyway it’s all a matter of projections in the end. Raycasting is also a projecting method, quite a literal one!