Tab targeting has been silently removed...

[Mblake81]

WASD feels inevitable today. Once mouselook became standard in 3D games, it made little sense (at least for right-handed players) to hold your left arm across your chest to reach the arrow keys. The WASD keys were more comfortable, and offered easy access to Shift and Space. But even though WASD seems like the obvious choice now, far fewer players used it 20 years ago.

Note: What does movement have to do with targeting monsters you ask? it is related to how you interacted with the game controls.