I have often wondered the same thing. Animals with white hooves usually have more foot problems. We have had lots of full Irish cattle over the years and I don't remember any that had white hooves. There are 3 Irish cows here now and all have very dark hooves. Both Dividend and Improver had dark hooves as well. I do think that there was more of a tendency for the Irish strain of Shorthorns to have hooves crack and to have sore feet.
Personally, I would never buy a herd bull with white hooves, as I have just seen too many cattle with white hooves that need to be trimmed regularly. Even if the bull had everything else right about him, I would walk away from him because of the color of his hooves,. Hoof trimming is not something I like to have to do... ever. I can't remember the last animal in our herd that had white hooves, probably because I try to select against it. As it has been said, quality starts at the ground up!
I have seen white hooves in many breeds here. We had Hereford cattle with white hooves and some Simmentals as well. It was when we were raising these breeds that I really started to pay attention to the color of the hooves. We had a couple of Swiss imported Simmental cows that required to have feet trimmed at least once a year, just in order to walk properly. After a few times of doing this, you gain a huge disrespect for them. There also were lots of white hooves in our Charolais herd, and I really tried to find Charolais herd sires that had darker hooves. That is not an easy task sometimes.
I am not sure why white hooves are so much softer than dark hooves. White hooves in wet conditions fall apart much faster than darker hooves. I have never seen white hooves in Angus cattle but some Angus lines have plenty of different foot issues as well.
I have no idea why this has not become a much bigger concern in this industry. I think it is pretty well known that white hooves are inferior to dark hooves, but I see people still paying little attention to selecting against white hooves. I know I have some commercial bull buyers who would walk away from buying a very good bull because of the color of his hooves.