Okay, I'll make a stab at this with my awl.
Due to the almost non-existent state of pouches from that time it is hard to determine commonality. The few with fairly solid provenance don't have any lining to my knowledge.
I believe one must also separate home made from store bought a well when evaluating any feature.
I'll agree with James on these points.
First I'll hone in on the fabric over leather as a liner. Most using fabric was most likely begun as a 19th century practice, but from whom, only I can speculate. From looking at today's contemporary's bag makers, including myself, items are lined to satisfy customer demands. Were they following the same customer trend in 1842? However, as more of our customers become more 'educated' to what is truly PC, unlined bags are beginning a comeback.
Now as to why lining MAY HAVE BEEN used 'in the early times'? Here are my humble opinions for discussion.
1. Used to add 'body' to a bag constructed of lighter leather, whether veg tan or not. Linings were probably initially applied to the undersides of flaps.
2. Used to 'quiet' the contents of a rather stiff, new veg tanned bag.
3. Used to make up for use of far inferior leathers to good cowhide, (squirrel, goat, sheep, ground dogs, etc) that did not take the day to day rigors.
4. Used as ‘quick fixes’ to items in No. 3.
5. Most in the rural probably didn’t know any better of what constituted a well made hunting bag IF they didn’t have access to better materials or techniques.
6. Probably used by quality harness makers/cordwainers as a means to do something better than their competitors. Yes, there was competition amongst them just as well there was between all the gunmakers to make something better. You can tell by reading old advertisers in colonial newspapers.
Any more potential reasons?
Gary