In the case of Brooks, I suspect the company has become aware of a "use it up and throw it away" among today's cyclists. They market their saddles to people who want a comfortable saddle today, not at some point in the future. Sure, there are those among us who complain the new Brooks saddles don't hold up the way the old ones did; but we seem to be a minority.
From my experiences in saddle discussions by touring bikers, I suggest that if using thinner leather is purposeful, it’s because of competition from makers such as Selle Anatomica, which is frequently touted as being comfortable right out of the box.