Often the "helpful" guys can be glory hunters, to the detriment of their own family, so the wife ends up picking up the pieces.
So, for example, it's Dad's turn to watch the kids on Sat and mum has a list of things she's going to get done whilst he does so.
Instead, Dad goes to neighbour's house to fix something and then they proclaim to the whole street how wonderful he is.
Meanwhile, mum is at home, watching the kids again, unable to do all the jobs she has planned.
Dad comes home knackered, falls asleep on the couch and when he's finally able to participate in family life, mum has to be up until midnight getting the jobs done she'd planned for that daytime.
Mum is resentful, kids have had to cope with a stressed parent, relaxing evening goes out the window, sex doesn't happen, dad doesn't understand why he's been "such a good guy" and his wife is annoyed at him. Rot sets into the marriage.
Couple divorce, dad still has his "good guy" image; mum is seen as unreasonable for wanting a life where at least she gets the odd day where dad parents his own kids.