I think it was mostly because the dukes wanted one guy to win, and all the regional lords voted for the victor, and obviously the dukes weren't too happy about that.
He got 13% of the vote, so either lots of people didn't vote, or there were a lot of candidates. Throw in the guys Family History, and there is a natural animosity between him and the Dukes, many of whom were instrumental in the down fall of the last realm his family ruled. Its not about who the Dukes wanted to win, its all about the guy that did win and long standing issues with that characters and his family.
