It could also be, Prue, that you are younger than some of us

I have two photos of one great grandmother (b. 1853) taken in 1904 and 1920s but none of the others, although I have a photo of another grt grandmother's (b.1842) brother and wife. I have photos of both grandmothers (b. 1873 and 1878) - first ones taken in the 1880s and others through into the 20th century.
Some younger members of RChat may even have photos of their great great grandmothers.
My niece, who is a couple of years older than you, has pictures of all 4 great grandparents and at least one great great grandparent.
It's all a matter of time periods and our ages, maybe.
Gadget
Added their birth years to make more sense!