Being nearsighted with astigmatism myself let me see if I can explain...
For the sake of explanation let's assume you are looking at a rabbit that is 50 feet from you. This is "the subject".
The OVF shows you the subject through a series of lenses and mirrors. This being the case, the rabbit appears just as blurry in the viewfinder as it would if you were looking at it without a camera. This is because the distance to subject is still fifty feet, the OVF is simply "framing" your view of the world.
The EVF, on the other hand, presents to your eye an electronic "picture" of the rabbit. Since the EVF display is only a few inches away from your eye, you see it in sharp focus.
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