Yep, good point. The reason is that the objective of the book is to cover as much material as possible, in the shortest time possible, and in the simplest way possible; so I had to build the shortest path between putPixel() and filtered textures, and that leaves things like antialiasing behind.

I explain a bit of this in the introduction, most of the time I present not the best/fastest algorithm, but the one that it's the simplest to understand. For example, I don't even mention Bresenham's algorithm; instead I present a super simple but inefficient one, which achieves two critical things: (1) you're drawing lines in no time, (2) it motivates the linear interpolation method that is then used for shading, z-buffering and texturing.