I don't think the police force of Crystal Lake has been particularly competent in any incarnation of the series, least of all the crappy remake. Chalk it up as another (bad) horror film convention.
In horror films, cops are one of three things:
1) hideously incompetent (most)
2) competent but shackled by office/city politics (Jaws, Predator II)
or 3) in on the horror (The Howling)