Why it matters is easy — insects are the bottom of the food chain: no insects = no food. The reasons are fairly easy to sum up in overgeneralizations as well: too many pesticides and reduction in areas where they can survive. But here are two articles with more info:
But this article goes into detail about the reasons for the declines in population and includes, as you’d expect from the National Geographic, beautiful photos. So just click thru and be amazed.