What do you mean, they typically get half the assets and a sizable chunk of the other partner’s salary in alimony that they don’t need to give up if they do become employed, and then if childcare is needed typically this would be an extra child support expense that both parties pay for even if the erstwhile stay-at-home parent has full custody.

How would the stay-at-home parent get a bad deal here?

If you can't afford childcare, getting half of the assets in a divorce doesn't amount to much. Divorce lawyers don't work for free either.