I am horrified reading about the American hiring process. I just read this and was like WTF 10 HIRING INTERVIEWS.
In Finland you are interviewed once. If you get a second interview it means you've been selected and it's about technical stuff like salary, benefits etc. I think this is because the interviewers are just regular bosses so the time it takes to interview is away from actual work. The prescreening of applicants is done by, shock, reading the CVs.
As far as my understanding goes, it seems to be typical that American companies outsource the hiring process. So if the hiring company drags out the process, they might milk more money out of the outsourcing company. Therefore it would make sense to have indefinite number of interview rounds. They could always say that it's because 'they want to make sure they thoroughly investigate people before hiring'. Does this make sense? Is there another reason?