Answer: "'Cause they like for you to see 'em streakin' !" Comes to mind...when you say this sounds like a joke. : ) ha!
However...I was actually serious about this poser. I must admit...it does appear to be a set-up for a joke. I must applaud your sense of humor, Leslie!
I have noticed for years and years that if the wipers are going to streak...they are going to do it at your eye level...no matter what. So that you have to peer over the streak or under it to see those wet morning traffic lights or tailights to a tractor trailer on the highway while driving through the rain during a cloudy overcast.
It can be a nuisance on a long drive to be bobbin' up and down around the streak to see what's going on. It seems to happen regularly to me...even after buying new blades. That is why I wonder: "How come the windshield wipers always streak...right at your eye level?"