You hear about kids peeing the bed…but do they ever POOP the bed? Why isn’t that anywhere near as common as peeing the bed?
Whoopi Goldberg used to poop the bed.
http://hotpz.com/2011/02/whoopi-goldberg-was-a-functioning-drug-addict/
““I winded up sitting on a bed for three or four days scared there was something under the bed. I wet the bed, I pooped the bed, I did all kinds of stuff and my roommate came back and said, ‘What is going on?’ I said, ‘There’s something under the bed…’”
And here’s a video.
Interesting question. IANAE, but I think bladder control is harder than bowel control in general, unless you’re sick. Bladders are small and the need to urinate generally comes on strong and quickly. Holding it in is easier for a twosie.
Hmmm, I’d posted a reply to this thread a few hours ago, but it went missing.
Noctural encopresis is relatively uncommon, occurring far, far less often than bedwetting, and tends to be associated with certain neurological disorders and also severe mental retardation and other brain disabilities, both inherent and acquired.
That, and we have to urinate far more frequently.
Which is of course the same thing you said (missed the edit window)
I think it may have to do with digestive processes slowing down when we sleep. It’s very common to need to pee as soon as we wake up, but pooping usually happens some time later (assuming normal bowel movements).
People pee more then they poop
Is there an award offered for succinct answers round here? I nominate this. 
I have no memory of this, but apparently I did this once when I was a little kid and had some kind of stomach virus. Mom ended up taking me to the emergency room while dad burned those sheets. Other than that I never had problems wetting the bed since I was potty trained and stopped wearing diapers.
My neighbor’s little boy once pooped his diaper during his nap, woke up and decided to decorate the nursery walls and rug with it. She used up a whole huge bottle of Mr. Clean getting that place clean again.
And usually if people poop in their sleep it is contained in the undies (if they are wearing any) and not as much a mess in the bed itself as pee is.
My daughter (not quite yet 3) has been potty trained for about 3 months now. She very, very rarely has an accident, but when she does, it’s always poop. For whatever reason, her bladder control is exceptional (she took one day to potty train…and was dry at night from that day onward…5 accidents during the training day, though), but her bowel control isn’t quite as honed. I think she doesn’t feel it as quickly and doesn’t have time to respond. She’s had two or three poop the bed accidents in the past three months, almost always during her nap (maybe one at night…can’t remember), but no pees now. I do agree with the above though…it’s usually not hard to clean up. She notices immediately, yells for us (feels embarrassed), and these few accidents only a little bit has come out, and has been very easy to clean up (toilet paper and plop). Wow…reading this over, this is a bit TMI, but it answers the OP.