Well, nasa and scientists are more interested in things 1000s of light years away in the galaxy and millions of lightyears away in the universe and for the telescope to make any use of those distant things the 'scopes have to be "far sighted" enough to do it at the cost of closer things not being as detailed.
For example, if you're looking at a galaxy 2-mill LYs away and the galaxy is decently resloutioned each pixel may represent may represent a light year, or depending on the size of the picture, it may represent millions of miles. Take that and look at something closer and that pixel representing millions of miles now has to represent 100s of thousands of miles. Our entire moon would be smaller than a pixel. I wonder, however, if it'd be possible to make a more "dynamic" telescope that can adjust its "sightedness" for the condition.
