I bet the expert woodmakers doing this job have very good reasons. Reasons that you haven't thought of..
Seriously, these people are experts. They probably know their job, really, really well.
This is just a random appeal to authority. If you would like to be constructive, please be constructive.
First, there is one person doing this. Or was. It was Jerry Lee, who recently retired. He did it for 30 years.
In fact, for giggles, i reached out this morning, and Jerry Lee says he is not an expert by any means in any of this. He was just a pattern maker who thought he could be helpful. He had no particular expertise in this when he started, and he would argue he is in fact, not an expert.
When I asked, he said they just didn't need to do it faster.
So it turns out no, they aren't magical experts trained in the artisanal art of ladder making with information passed down from the ages, and no, there are no magical reasons that only the wood cognoscenti have thought of. Sorry.
They just use the forestry handbook data and info like everyone else!
There is your really good reason.
It may come as a surprise, but this really is engineering. People have been studying wood as an engineering material for a very long time, and there are a large number of published studies on pretty much anything you can think of from drying rates to density to you name it.
Take a look at https://www.fpl.fs.fed.us/products/publications/several_pubs...