How about "because that is the way locks like that were made?" These complex systems on fine European examples have almost nothing to do with what the vast majority of locks imported to or made in American were like. My long departed friend Lynton McKenzie concluded that most of those "features" were just gimmicks designed to sell locks.
Gary
That there were a lot of gimmicks goes without saying. I have seen newpaper cartoons for the time that lampooned the patenting of various improvements by showing a "patent" gun that killed in all directions at once. Fellow hunters, dogs, everything.
But some the the stuff apparently works. The Nock breech for example, while not as fast as some is very reliable and more importantly more CONSISTENT in Larry Pletcher's tests. Consistent lock time makes wing shooting easier. What most of the improvements were trying to do. They had little interest in rifles, the real money was in shotguns.
The rollered frizzen/frizzen spring, the smaller lock parts both internal and external, the stiffer springs and the longer distance from pan to frizzen pivot all make a difference. The recessed breech is supposed to be faster since the pan is closer to the center of the barrel, but this would require Pletcher to do some timing. The V pan, the swoopy "wave" pan etc etc were just window dressing I am sure. But the vent wiper may well have helped waterproof the vent. But then we have the art value. When selling to high end customers looking fast can be as important as being fast.
My 16 bore rifle with the lock made from Manton recessed breech castings is very reliable. I almost never have to knap a flint, when it quits working the flint is generally used up and knapping only gives another shot or two. It gives good flint life even though it has very stiff springs. It also jars the rifle less.
Of course they were not used on American guns to any great extent, but Simeon North used them so some were used.
I like them for a couple of reasons, they work really well, they are mechanical works of art and they look good. If the firearm is acceptable with one they are a great choice.
It is obvious that a 1800-1820 lock is incorrect for a Colonial rifle, but where they fit I really like them.
We must remember the high end English guns were made for a far different clientele than most American gunsmiths worked for. Money was no object to the people buying the high end guns.
Dan