Sadly it's easier to just call something interesting than to explain why it is. Partly this is because "interesting" (or "fascinating", "thought-provoking", "intriguing", "notable" etc.) is just one word, and it's easier to write one word than a sentence. More important is the fact that you probably don't know why you're interested by something until you do some thinking about it.
Reading this, I couldn't help but be reminded of a conversation between two of my academic advisers, quite early in my graduate linguistics studies, about Chomsky's use of the word "interesting" in that he tended to use it as an insult. We had formed a reading group one summer to discuss The Minimalist Program and discovered that Chomsky would boldly proclaim that one topic was "interesting" while another was not, seemingly by fiat, with little or no explanation. Our group consensus was that what he really meant was that a linguistic topic was "interesting" if it helped him make his argument; it was "uninteresting" if it did not (we came to the same conclusion about his notion of "narrow syntax", btw; this wiki page lists a variety of other criticisms).