the accent issue

I've read many a criticism of American sounding Gere surrounded by a plethora of primarily British accented actors around him. Say what you will about Gere's performance overall (which I had no issue with), but I don't quite understand the criticism about the accent in and of itself. I have more of an issue with Gere's accent (i.e. trying to sound British) going in and out. I do admit that he sounding different than the largely British case a bit off-putting, which I blame on the casting director. All I'm really trying to say is that if we're talking about authenticity, why is or should be a British accent considered more authentic to 1,000 B.C. Israel than an American one?