Some companies tent to keep 2 people in the run for a long time. When you start noticing that after your second interview, nothing happens, only when you ask, you get some hints that they are still interested in you, then you may presume they are negotiating with someone else and keep you as a backup in the the first choice doesn't work out.
But in other cases, I think companies may praise themselves lucky that they find suitable candidates at all. In my company, we are situated outside of the city and they sometimes have trouble finding good candidates at all.