Most of us teach in highly imperfect labs. A big screen that lies flat against the wall.
Many labs have screens that are too small.
To display the high level of detail on a web page, screens have to be sufficiently large to be seen at the back of the room. They need to lie flat against a wall so that they don't quiver from air circulation and distort the image. Projector light bulbs have long lives, but after several hundred hours they slowly start to lose brightness. Just because you can see something on the screen doesn't mean you can see it well, and this can cause considerable eyestrain over several hours. It really DOES matter what side of the screen the instructor is on.