We must keep in mind aliens are, by definition, from another planet.
Their vision (if indeed they use optical vision at all) might work in such a way that what appears blurry to us is absolutely mint for them.
They are probably flying around like OMG WTF at the fact that we don't get it yet.
"silly blurry humans" they say to each other. That's why they abduct the odd cow. To see how it's eyes work. Of course by tailoring their appearance for cow vision, they are still blurry to us.
This will be fixed through the channels of trial & error in time.