This is a landmine question. I was let go from my last job and 2x's in interviews I have cratered on this question. Best option from my standpoint, "a new management team came in and they are bringing in their people". This in my opinion is best so your not saying "it didn't like my boss" which make the employer thing "what if they don't like, they might just leave". Best to put it on the boss that they came in and they are bringing in their people.