When you look at a monitor, you're looking at a quad at a set distance. Your eyes are focused on that quad in the exact same way they would focus on anything at that distance.

In VR, dynamic depth is simulated using stereo-screens where each pupil is pointed at a dynamic focal point BUT stero-focus is not the same as lens focus. Because of this, VR produces a disjoint sensation where stereo focus changes to the simulated position but lens focus remains fixed.

You can experience the difference by holding up a finger and looking at it, then look at a distant object. Notice that you'll see two images of your finger as you focus away. That is stereo focus. Now do the same while covering one eye. Notice that the finger is now blurry but not doubled. That would be the lens focal difference.