The big mystery throughout the whole film is "What is up with the women in Stepford?" Joanna thinks that something is badly wrong, because these woman think about literally nothing besides carrying out tasks for their husbands, keeping the house clean, etc, etc. Joanna's husband just thinks that all those men got lucky. It is clear to the audience that something is wrong with them, the Stepford wives are just not behaving like normal woman. Like normal people.
Nobody is that excited about the weekly grocery shop
The mystery of "What is up with the Stepford wives" is answered by the end of the film. They have all been replaced by attractive Roombas. The mystery that never gets solved, the big massive hanging question that is never, ever answered during the entire film is this:
What the HELL is up with the Stepford husbands?
Why would anyone, seriously, want to be married to a robot? Some people may have a fetish in that direction and if so more power to them, but the majority of men tend to be more attracted to actual people. True, the women of Stepford still look and feel like real women, but they aren't, and they aren't in a way that is blindingly obvious to anyone who regularly interacts with them, like their husbands. They are slap-bang in uncanny valley, and it's hard to see what's attractive about them besides the (slightly fake) looks.
In the film, Joanna and her husband show all the signs of being happily married before they get to Stepford. She's a photographer. She talks about philosophy. She looks after the kids well enough and does enough housework to keep the place vaguely tidy. He seems OK with that. Yet a few weeks after moving into Stepford he's asking her to quit her job and complaining she never keeps the place tidy enough.
To be honest, I was starting to wonder at that point whether he'd been turned into a robot. That would have been a nice twist.
It's not enough just to say "every man secretly wants that" because that denies ~50% of the population basic human feelings. Most people ( both men and women) marry because they genuinely want to stay with someone for the foreseeable future. Joanna's husband married her for who she was, not because he secretly wanted to marry a robot but couldn't find one in New York. When Joanna's friend suddenly turns from an outgoing woman into a perfectly-polished Stepford wife, her husband seems unfazed. More importantly, neither men seem to care about what affect replacing their wives with a well-programmed games-console in a frock will have on his children. No matter what people think "all men want" it's generally agreed that it's better for kids to be brought up by actual humans than computers that can only converse about washing-powder.
And bear in mind that the whole premise of the film involves the women being killed before they are replaced by their robot-counterparts. Which means that a whole group of men suddenly decided it was a good idea to murder women that they had been previously happily married too, often for many years.
The Stepford men are as unnatural as their pretty talking-Roomba wives. They all are happy to commit murder. They all completely change their ideas about what they want their wife to be about three days after entering the town. By the end of the film, they are all happy to be living in what is essentially a giant sausage-fest with some very pretty electronics - men and children are now the only humans in Stepford. They can never talk, laugh or enjoy time with their wives again without being constantly aware that the laughter is fake, the excitement is programmed and the woman that they pledged an eternity of love too has been murdered and buried under the patio.
There is something very, very, wrong with the Stepford Husbands.
And we are never told what.