Totally anecdotal, but the people I know who have trouble managing money are just completely unaware of it. Money goes in and money goes out, and they only do something if someone calls them or sends them a letter. As soon as you show these people the numbers, they get it. It clicks for them.
Mint and Penny both suffer from the same thing those "hire a maid" apps suffer from; Once I've made the initial contact, I have no reason to continue to use the service, I can just contact the maid directly. Same thing with Mint/Penny; Once I am shown my finances, I have an awareness of my financial situation and don't need the service any more.
What will drive me to continually use this service, beyond my initial few weeks? You can only analyze my finances so much before there is nothing left to tell me. And then you will get to the point that Mint is at, where you start offering me credit cards and credit reports and mortgages, because that's the only thing left to do in this space.