probably because it's american company or something
the actual maps go back farther. if you se tthe timeline from "past-1750" or whatever you'll find very old maps. i think what needs to be improved is the inerface to select years from befroe 1750. i think the earliest time on there should be the year of the earliest map they have available. but here's like brittany and normandy from like 1633 that i found using this resource
http://biblio.unibe.ch/web-apps/maps/zo ... pg&col=ryh