I wonder if your optometrist is either lacking in confidence in his/her ability to take good pictures without drops, or just being lazy? As we often find, there are good and not-so-good GPs, nurses, dentists etc., so probably optometrists too, unfortunately. When I had mine done (only had it done once) the chap did take a good look first to see if he could take them without drops, but decided he needed them - at least he considered it!
He seems to be a very good Optometrist. He spends ages looking at your eyes and makes sure he get's all the usual tests done thoroughly.
How do they check to see if they can take the photo without drops?