Why does the Human Resources Office keep sending all these slackers to work in my department?

S**t flows downhill my friend.

It's your job to write a job description that slackers cannot be seen to qualify as candidates.  HR just wants to fill positions expediently.  They go by what the department requests.  I am trained, and have trained managers how to write descriptions using the proper words to get the opening assigned the pay grade  they  prefer.