Move, shoot, and drive are easy, or at least well worked out, and everything else is hard. Doors are just a common case of "everything else" Sitting down realistically is hard. Standing up realistically is hard. Picking up stuff realistically is hard. Interacting with any object via contact is hard. Interacting with moving avatars is really hard.

The hard problems come up when you actually have to do motion planning, in the robotic sense. Few games do that. In most games, you're just moving the avatar while running canned animations. UE5 has a new dynamic animation system which is supposed to help with this. In the UE5 demo video, you see the character walk through an open doorway, and she reaches out and touches the doorframe. That's some kind of IK-driven animation triggered by proximity. Not clear if the mechanism behind that is general enough to handle door opening. Anyone know?

In virtual worlds, where you don't have pre-planned gameplay, it's a big problem. Second Life has hundreds of thousands of doors, and at least three vendors of door control software. Usually, doors have to be clicked on to open them, although stores often have automatic sliding doors.