Simply because it is quite difficult to explain the concept in writing. They might have a different point of view as to the quality of your work. Or they may

Simply because it is quite difficult to explain the concept in writing. They might have a different point of view as to the quality of your work. Or they may have taken other factors in consideration (your portfolio, communication style, etc). But not contacting you with any kind of a status afterward is definitely shabby, on their part. And asking you to do a second assignment without taking a moment to evaluate your first (and apparently without bothering to tell you in advance that not one, but two or more "quick" assignments would need to be done), all the more so.