Most places send secondaries to EVERYONE. A few do "screened" secondaries where they only send you a secondary if they are interested in you. If you don't get a secondary, you probably won't get an interview either. (There are a very few exceptions to this.) Most of the time everyone gets the secondary, the institution pockets a whole bunch o' money from folks they have absolutely no intention of interviewing.
And, btw, secondaries cost. Up to $100 each. In addition to the primary fee.