There are all sorts of possible reasons. One very likely reason is that the person using the software doesn't bother updating the status. It doesn't benefit them, it takes time, so why bother? It gets put on a back-burner and done later, or not done at all.
Another reason is that the person in charge of going through resumes is busy with something else, is out of vacation, is sick.
More common reasons from DJClayworth: It actually takes more than a month to receive and process applications; The company continuously posts job ads to find good people, but only invites you for an interview when it actually has a vacancy; they have some good candidates they are interviewing, but if they don't work out they will ask you.
Sure, it's also possible that they asked for resumes for a job they don't need filled until later, but that is much less likely than the other reasons.
How does it change things if you know why the status is not updated? It really doesn't. The best way to not fret about jobs applied for is to apply and then move on. If they call you, great. If they don't, you were already looking at other jobs anyway.