I think most of these type of shows use a bit of "artistic license",however some people do live in really unclean conditions,and don't realise it.
I had a school friend years ago who lived in an absolute tip,his mother never cleaned,and his old man worked away most of the time.
One day we went round his place,and his dog (a big slobbery labrador) was lying in front of the fire motionless.We asked if he was ok,and our mate said he'd been dead for 3 days,and they were waiting for the council to come and move it!
His house became so bad that a gang of us used to go round,and clean it every week.