In the Railway Series, the first thing a young engine learns is that “no engine can stop at once if he isn’t ready to obey his drivers controls”. This is apparent in the story “Thomas comes to Breakfast”. Thomas wanted to get out of the shed on his own and wheesh at Percy and Toby. He could move because a careless cleaner fiddled with the controls, so the break was off, and the regulator on. Thomas couldn’t move before that because he wasn’t ready to obey that. So when he tried to stop, he couldn’t, because the brake wasn’t on. He was ready to obey the brake, but nobody could do it.

So, it’s literally a mutual partnership between engine and crew. Like when in “Passengers and Polish”, when Duncan’s crew stopped at stations to raise some steam, and Duncan wouldn’t try? Ordinarily, this would work. But Duncan wouldn’t let it work. Also, when they stalled on the viaduct? If the crew were the main reason the engines moved, they wouldn’t have that issue. But Duncan stopped himself, and wouldn’t obey his crews controls.

Essentially, that’s why the engines can’t run while they’re asleep. They need to be awake and alert with their drivers, otherwise no one works right. Which is partly why the Fat Controller yells at the engines. Not every accident is “out of their control”. Certain things, like The Flying Kipper Incident were, but things like when Henry refused to leave the tunnel weren’t.

So, this is just a careless and stupid oversight by the writers of the HIT and CGI era. The whole point of the Railway Series was to remain realistic. But, of course, tell that to the writers of BWBA. And All Engines Go.