Nobody knows why. I've asked the same question repeatedly since this case started. I also went as far as to predict that this lack of searching is going to flip around and bite LE right in the *advertiser censored*. If it comes to light someday that she was lying in a drainage ditch close to her apartment for the last 6 months, people aren't going to be pleased. Many people volunteered to help search, but were pretty much told to stay home and play on their computers instead.
I don't know what theories LE has pursued in this case, but I think they put blinders on way back in the beginning, developed a theory, and refused to budge or deviate from that theory.
Obviously that plan of attack hasn't worked, otherwise she would've either been found or be back home by now. Simply put, if their investigation was yielding any results.......at all....... there would have either been an arrest and/or her whereabouts would be known. Just stamp it a HUGE FAILURE and move along...........................we'll have to wait and see what happens in the spring when some little blue-haired old lady is out walking her chihuahua down a well traveled path in the park, and he walks up to his master with a finger in his mouth.