The resumes of people straight out of college/university are often horrible, so this is more likely than you think.
I don't know why that is though, it's obviously important. Maybe these, err, kids, think that as they have no working experience, employers aren't likely to look at it a lot?
It's really hard to build a resume without having experience (in both your career and in creating a resume). When your main accomplishments consist of taking classes in your field of study, what do you put down that is both relevant and not too much information? How do you predict what the company wants to see on a resume when many job postings flat-out lie to you, puffing up the job and inventing requirements that don't actually exist? How do you emphasize that you know these skills but don't have any concrete evidence beyond a degree to prove it?
It can be done, obviously. But making a good resume is a skill that generally take time to master. If you do it right the first time, you may never need a resume again. These difficulties are why career services exist at colleges. And even they can't get it right sometimes.
My exasperation comes from the CS field interviewing recent CS graduates. Many don't put the personal/hobby programming/adminning/etc projects they have done on their resume. The result is a resume of less than half a page that lists their name, study and hobbies (outside CS!). And sometimes with sloppy formatting & layout.
They presume "it wasn't real work" so it "doesn't count". I'll be the judge of what counts!
If your hobby (programming, Arduino, security research) is relevant to your industry, it's a great way to tell people that you know and are interested in something without making it the main focus of your resume.
If I'm applying for a network administration job, knowing the Linux source code wouldn't be required but you'd better believe putting "hobbyist Linux programmer" would do nothing to hurt your chances of being hired.
Aside from what the other poster said about work-relevant hobbies, having hobbies on your resume can be handy for the interviewer. It allows some chit-chat to put the candidate at ease.
It's typical here to put them at the very bottom. I've have interviewers in the Valley use the put-at-ease technique on me, so it must happen in the States too.
More likely they haven't built up enough experience to know how few of the things they learned about writing resumes in college really apply to a job search for a serious technical job.
I don't know why that is though, it's obviously important. Maybe these, err, kids, think that as they have no working experience, employers aren't likely to look at it a lot?