Turret production

[modelbouw nederland]

Hello everyone,

I have placed another question some days ago about the production of the B1 Bis I believe.
Now I got a more specific question about the production and design of turrets for the French tanks.
Because, I'm reading in the sources that I'm using for my research, such as the book Trackstory about the B1 and other variations of this tank.
That the turret was the most expensive part of the tank to produce and the most difficult to produce.
Why was that? Because, to me it look a really simple design and not to difficult to produce either.
And why was the turret so cramped and not that well designed for the ergonomic side of things?
I mean, as I can see on the video of the Chieftain inside the B1 Bis.
It wasn't that great to be a commander in that turret in that tank.