is there actually proof that "indoor dining is a huge cause of the spread of the disease?" (i'm not disagreeing, i could google it i suppose).
Yes.
Tables being spaced out doesn't do much if you're indoors. The virus is spread through the air. The initial belief that it is only in droplets that fall to the ground within six feet was wrong, and that has been known since very early on. The CDC was slow to update their guidance but eventually did last fall.
There have been many tracing studies that show how workers or people in restaurants were infected by someone who was way across the room. Any time spent indoors where you're sharing the air is dangerous.
Wearing masks helps this a lot. So working in a building while everyone is wearing a mask is a lot less risk than without masks. But when eating in a restaurant, you take off your mask. You're also talking a lot when eating in a restaurant. Talking, singing, coughing and things like that expel viral particles much more than simple breathing. So that's two problems with indoor dining that make it even worse than other reasons people end up indoors.
The sad thing is that we've known that airborne transmission was super important for a really long time, but the official guidance has been so lacking that people still worry ten times more about sanitizing surfaces than about proper ventilation. Plane flights are less risky than other public transportation because they have such great air filtration and recycling already. If we had been working on improving that in restaurants starting ten months ago maybe they would be safer. But the leadership everywhere has just been so lacking. It's extremely frustrating and literally hundreds of thousands of people all over the world have died because of it.