One reason for have the native material "humped" in the center and the end of the ties exposed was to promote drainage away from the ties. This technique was used on many railroads built during the expansion era of railroads -- beginning with the end of the Civil War and continuing to the turn of the century or later.
Of course, if and when it could be afforded any material like rock ballast that would allow water to freely flow through it was preferred. I have not been around cinder ballasted track to know if it drains in a similar way.
Brian Norden