FF EOS film SLR's came long before crop DSLR's, and when DSLR's came along, they used FF lenses from the film Era. The first DSLR's were APS-H. Their were no special "digital" FF lenses that were not interchangable on film bodies, anf still aren't!
However, it was very difficult and expensive to build high quality FF lenses at 10mm. It is possible, however to design lenses that sit closer to the film plane and have a smaller image circle for a lower cost. Some of the lens elements might hit a FF mirror, however.
Thats why the EF-S lenses were designed to be incompatible with FF, in 2002, there were still lots of FF film cameras in use and Canon did not want people damaging their camera.
Early Canon Crop cameras, D30, D60, 10D only had FF lenses to use, and this caused a lot of complaints from users wanting very wide angle lenses.
Lens technology has evolved, and it is now practical to make wide angle lenses that work with crop bodies, but it would be very confusing to create a third Canon EF lens type.
Canon made Film SLRs before they made DSLRs!!? How has this been kept a secret? -Just Yankin your chain. Yes, i understand that Canon's First DSLR was APS-H. But what about the The Canon EOS DCS 3? It was a 1.7X crop and came out in 1995, six years before the EOD 1D. I wonder what kind of lenses it used?
And maybe it's just me, but looking at Canon's naming conventions of 1D-1Ds, Mark this or that,5D, 50D, 500D... I can't imagine they care about confusing people. What is the plural of 1Ds ? Imagine standing at the Canon drive through and trying to order; Yea, give me 5 1Ds, 5 1Ds-es and 2 5D Mark IIs.... What? Um Yea, and one EOS Kiss Digital X. (A japanease 400D)