As to appealing to the "tiny American audience", Who has had a HUGE pop-culture impact, Who references are in the media a lot these days. Why not build on that?
Because he's not paid to boost BBC America's ratings. He's paid to make a show for British Licence Fee payers.
I don't get it.
More people watch in the US, more revenue to BBCA
More revenue to BBCA, more revenue to BBC
More revenue for BBC, a better case for booting the series budget rather than cutting it.