>- Why does this piece of work need to be done in the first place? Why would a backlog be limited to 3 months?
If it's a literal factory they may want minimize storage costs. You have to rent space to keep the product until the customer expects it delivered. I'm a layman so take my guess with a grain of salt.
> (As someone else pointed out, a variable whose value changes once in 10 years probably doesn't really need to be a configuration parameter, though making it into one probably counts as a slight improvement.)
I'd argue that adding a variable that changes once in 10 years is not an improvement. Config files should consist of things that actually need to be configured. Adding crap you'll never touch makes it harder to find the variables that are actually important, and also makes it harder to read and understand all available options.
Introducing configuration variables for the hell of it is analogous to writing every method to be as generic as possible; useful but not worth the risks and expenditure. Just like how we often draw the line and say "this method doesn't need to be any more generic", config variables similarly need an approach more nuanced than "move everything to the config file".