I think it's beacuse he has a big ego, a touch of arrogance, he is very confident in himself, outspoken, passionate and can be deemed to be a bit confortational from time to time. All that can rub people up the wrong way, people seem to love him or hate him and there appears to be no middle ground IMO.
I think he is a great appointment and I happen to think he will do very well here, I felt good as soon as Sherwood was appointed which I never had with McLeish or Lambert.
A bit like Mourinho!