I know at a restaurant where my friend works that To Go Orders were assigned to a member of the wait staff.
I think this is more about standardization than anything else. Their CC slips have a line for tips since most of their business is in-house. There would be additional cost to remove that line for take-out orders (where they are less likely to be able to make money by upselling, selling alcohol, etc.), so they just leave it. When I was making money hand over fist and had no kids, I tipped for take-out. Today, not so much.
This kinda crap irks me. The whole reason I order to go is that I don't want to have to bother with the crowd, wait staff, etc. You don't get "service" when you pickup a togo order. Now, if the restaurant places a waiter/tress to cash out your order... then that is the fault of the restaurant, and it shouldn't fall on the patron to "tip" someone for approximately 30 seconds of their time. Hostesses should be taking care of that stuff, honestly... not wait staff.
A lot do it because they may do delivery/dine-in. They also do it at places for the cooks or preparers. I've tipped on a pizza pickup before because the guy was so nice while I was waiting. I tip at places like Cold Stone. I also tip for carside to go, especially if the weather isn't nice. When my wife worked as a ToGo specialist at Olive Garden, she received tips all the time.
I can understand the feeling. When I worked I always make my rounds as a waiter so the customers can holler at me if they needed anything, but I've definitely eaten at places where I don't see the waiter/waitress except when the food/drink's brought to the table. This is especially true since I'm a young Asian, which does typically get stereotyped into being bad tippers. Still, that is "service". So you should leave a tip. Preferably, you should mention this to the manager rather than just leave a $0 tip. The former shows you're concerned about the service. The latter shows you're an a-hole. As for automatically tipping a large party, that is necessary for the sake of waiters not quiting. As mentioned with the "after church crowds", you can have large groups of horrible tippers. And large tables take up a lot of a waiter's time. And could just screw the waiter's entire day if they don't tip well.
