Complexity. Digital AA is very hard to design, just the mathematics involved are extremely difficult to grasp, much harder than analog. Aliasing shows up SPEC

Complexity. Digital AA is very hard to design, just the mathematics involved are extremely difficult to grasp, much harder than analog. Aliasing shows up SPECIALLY in purely digital systems. Take a sample every half period of a periodic signal like a sinusoidal wave. Your signal output will be constant or zero. Take a digital sample(calculate a frame) of a wheel in a 3D game (draw the wheel at a specific position), each 30th or 60th of a second. The wheel will go backwards at some speeds(stroboscopic effect, a form of alias).