Why wont the vet let me be in the room when they euthanize my rabbit?

I recently went with a friend to put her bunny down. I arranged everything which means i had to call around alot. When i talked to them almost every vet office told me they wouldn't allow you into the room when they euthanize. Or if they do it costs twice as much. This sounds VERY fishy to me.... Any idea why they won't let me be there for my bunny when it's her time to go? If they are doing something shady behind closed doors I'd rather pay 2x as much to be there and make sure she doesn't suffer. Thoughts?