I remember one of the more recent Doctors commenting that pretty much from the day they were announced they were being asked almost daily "Yeah, but when are you leaving?". All they can say is something non-committal, because that's the way it is.
It reminds me a bit of when some tabloid showbiz hack, in the News of the World or the Mirror or something, ran an "exclusive" that the Spice Girls were splitting up, and every time after that they released records or went on tour or anything like that, they would say "The Spice Girls, who I exclusively revealed are splitting up", and this went on for months and months, maybe even years. I mean, they were going to be right eventually.
That's a bit of an oversimplification, if you look at two of the biggest dramas in the world over on Netflix in Stranger Things and The Crown, both have had no new episodes in 2018 despite a far higher budget. Money does not solve all woes.
Well, yes, and I don't really know why we have to have a new series of Doctor Who every year regular as clockwork anyway - no other drama works like that these days. The new series of Luther is the first one for three years, Doc Martin usually appears every other year, and virtually every other drama on TV is broadcast when it's ready. It used to be the case in the seventies and eighties that dramas would appear at the same time every year, but no longer.
The suggestion is that if they wait too long the kids forget about it, but surely they just watch all the old ones over and over again? That's what they do with Harry Potter films and Star Wars and the like.
Rather good Doctor Who episodes when they're ready then some rubbish episodes they'd had to rush just because of the idea there has to be a new series every year.
KELGE, Amber Avenger and DE88 gave kudos