Perhaps it has something to do with the type of gun and intent of its use. In the 90's I was designing and having built benchrest standard varmint rifles with wooden stocks (good synthetic stocks were still in the future). The importance of controlling the harmonics of the action and barrel were just beginning to be understood and with it came glass bedding, pillar bedding, aluminum blocks and as part of the accurizing process, sealing the wood to prevent any swelling or warping. That included the inside of the action, barrel channel and under the butt plate along with all other exposed parts.
A 100 years ago shotguns, as they are today, are not accurate instruments and I expect it was more important to allow the wood to breath in the various conditions it was exposed to to prevent it from over drying or rotting and resultant splits and cracks.
