If it’s becoming a big issue, why not ask people to put a credit card on deposit when they sit down?

Restaurants that see you pay after the event are really in the experience business. Putting a card down takes away from the experience.

That's not a problem, as such, when all restaurants are doing it, but it's hard to go first as it compels customers to go elsewhere. Which you especially can't afford when dine-and-dashers are already hurting you.

It will likely go that way eventually. But it's a big risk and will no doubt claim some casualties when it comes.