Agree with this. It must be brutal having to step up to elite level dance training as a regular (albeit celebrity) punter. It's likely unbelievably hardcore training, but a level that elite dancers are used to and thus feel is socially normal, but that regular people are shocked by and have never been exposed to.
You probably need to push the hell out of a person to get anywhere. There's likely relentless pressure on the dancers to upskill the celebs to put on a good enough show and likely there's some necessarily true blood, sweat and tears going on there.
I think with these shows, it's the culture to blame. The celebs need to know how hardcore it will be before they sign up. Stuff like Celebrity SAS, well the clue is in the name. But Come Dancing sounds all cutesy and nice, but really it's probably Celebrity SAS just with dance shoes on.