This is a completely random question, but why don't post-op women use speculums to dilate? It seems to me that a speculum that can be "opened up" once inserted would be a great way to actually maintain depth and build width, as opposed to hard and progressively wider dilators. At a minimum, maybe a speculum could be used prior to inserting fairly wide dilator.

Why is this wrong?

A speculum has relatively hard  tips and would not work well for maintaining depth (look at a photo, it will be immediately clear why this isn't what you would want. They are also designed with the lower limb having greater depth than the upper, I assume that's so as to reach the anterior fornix.

I had a pelvic exam just a couple weeks ago and experienced that the tight spot I have about 1" shy of full depth registered a really sharp *tweak* as my doc opened the instrument. I prefer regular dilation (which now I am doing almost exclusively using sex toys).