It's because you are not yet in active, progressive labor where the inevitable conclusion is birth. You're not yet at the point of no return, if that makes sense - if you were in the runaway train part of labor, you would have contractions getting closer, stronger and would be dilating. Better to just go home and let things happen. The contractions could go farther apart, stop entirely for a while, etc. If they keep you, they'll start interventions and those aren't good for anyone. Take a nap if you can. If you can't sleep, then walk around, read a book, fold some laundry, whatever. With my first I was sent home from the hospital because I was having contraction but despite being somewhat dilated and effaced already, and being 41 weeks and 6 days along, I wasn't laboring enough. So I went home for the day. Unfortunately, I had to go back that day for the first part of my induction (which was scheduled to be an outpatient procedure and then I was to come back the next day and deliver) and they did decide to keep me, start interventions and we had my very long and rough induced delivery begin. If I had known then what I know now, I wouldn't have gone back that day or I would have gone for the cervadil and had insisted on going home to wait for labor to progress.
Anyway...have patience! You're very close. Trust that when progressive labor begins, you'll know it. Hope that your delivery is fast and easy and that you meet your little one very soon!