How are the BBC not responsible?
They are responsible, whichever way you look at it, either for cutting funding and messing Moffat about, or by not dealing with the situation if it is Moffat's doing. To suggest its not the BBC's fault in any way is to imply Moffat is some kind of evil manipulative genius who makes Jimmy Savile look like an amateur (in the pulling wool over people's eyes, not messing with kids kind of way obviously!)
I think it can be safely assumed we haven't had 2 split series in a row because Moffat is lazy and incompetent. He'd really have been fired by now if he just... failed to deliver half of the episodes he was meant to per series. I can't imagine his employers forgiving that so casually.
It's the BBC's fault. They'll waste money on all kinds of crap but be tight Ferengi when it comes to Doctor Who.