Although it would be good to see someone's karma with you. If I've downvoted someone more than 5 times, I'd like to know so that I can just block them.
But tags and labels on a user require an extra step on my part and it doesn't really integrate into the flow of the site. Karma score is just part of how the site works that requires no more extra effort on my part, as I was going to up or down vote them anyways.