I think a major reason is because the majority of the work available to new grads is part time, and there are more females than males who are willing to accept that as an outcome. Many females actively seek part time employment after graduation, which works out well for them. Not so good for the males who need to work full time, since those positions are vanishing at ever-increasing rates, and that rate will only increase as the new programs start graduating newly-minted ODs.
The writing is on the wall for anyone who chooses to see it. Optometry, as a solid profession, is on the way out.