I think only the person who develop the apps gets the profit from the ads and those who work on the app does not earn anything.
Most probably. And if someone is in urgent need of money, it's not advisable to turn to 'money-making apps' as a source. It's still better to have a job where you're skills will be paid. It's also more rewarding.
I don't know if flipping burgers is more rewarding and I really doubt it's less stressful, but it's definitively more profitable. People doing these apps just don't value their time, if they did they would not use them.