I share your hatred but that likely isn't what is happening here.

Put simply, someone fucked up. At an airport, the competing concerns of health and security are in their most extreme tension. For some reason, someone on staff skewed security when they should have skewed health.

There is no excuse for it, and guaranteed it has already been resolved or soon will be. This is in one of the busiest international airports in the world, and masks are still very common in air travel, particularly from countries like Japan - and I believe this restaurant is even in the terminal that ANA flies into. Restaurants simply cannot afford rent if they intentionally impose restrictions like that on their customers.