Q: If the goal is to raise funds for worthy causes, what's to stop a shop from making a game be super easy, such that you'd have to work at it to lose. Wouldn't this maximize funding?
A: Remember the model: you're in competition for company profits, and if your heroics are insufficient to save the day, then wish your peers better luck. The company cannot afford to just funnel any amount to worthy causes so "game difficulty" is how to apply the brakes and really make the games instructive.
On the other hand, there may be times when just taking a survey, answering a questionnaire, is sufficient to have the proceeds go to such and such an agency, perhaps with matching funds. It's possible to have a game time out when various goals are reached. No one said they needed to be open ended.
Q: I don't get why I'd want to play in a coffee shop, especially one that serves adult drinks, when I could play the same games at home, and spend less on beverages.
A: you're free to stay home. Some find the conviviality of a shop appealing and are looking to others for tips. What's the hot new charity to be connected with? Remember that people compete with their profiles, with "cooler than you" a motivation (friendly rivalries, looking good on the runway of life... showing off).
Also, depending on your zip code, your CSN affiliate may have access to ingredients you can't easily get as an individual (ayahuasca for example). Again, you might want to seek guidance, check LCDs for workshops and meetups.