Obviously you have never tried to find something the size of a penny looking at it from 25 miles away (similar ratio of the size of these new moons from earth) in near darkness. With more and more advanced technology (significant improvements in telescope power even in the last decade) you can find smaller and fainter things.

Yes we sent a probe to Neptune but when you aren\'t expecting to find things you typically don\'t unless they are big or near something else you were looking at (i.e. in the case of the 6 moons I believe most were near Neptune\'s rings).