The implication is that since both people in the household work, they don't have time to cook their meals. If you wanted simply to correct the given sentence you would need to include the infinitive form of the verb "be." In this way the sentence would read, "The rise in dual-income households has caused many families not to be able to cook from scratch." Although grammatically correct, the sentence still sounds stilted, unidiomatic, and unclear. It would be better to say something like, "Since both members of the household have full time jobs, they have no time to prepare home-cooked meals."

I would say: The rise in dual-income households has caused many families *to not be able* to cook from scratch.

You're welcome. If you would ever like to schedule a lesson, let me know. I'm new to Italki and am trying to get more students. Thanks!