:hatsoff: to Hawkeye2 for an excellent reply!
In our period of traditional muzzleloading, the spike bayonet was most popular for a number of reasons.
As Alden mentioned, the Plug Bayonet was usually a spear type point or blade, but you could not reload with it in the bore of the musket.
I cannot document this, but no doubt they chose the spike bayonet because it would not get in the way as much as a blade when reloading and a blade on the end of a long musket would have been VERY difficult to make effective use of slashing with a blade bayonet. Socket bayonets were/are a LOT easier to get penetration with than blade bayonets and takes less training of the Soldiers.
Blade bayonets did not become very common until they shortened musket and rifle barrels to "Two Band Length" in the 19th century. The Blade was meant to make up for the shorter length of the 2 Band Arms vs a 3 band with a socket bayonet and supposedly sometimes to be used as an Infantry Hanger or Short Sword. Of course they didn't seem to TRAIN soldiers much with them being used as swords, as a general rule, and that made that point moot. Actually, to get the best out of a blade bayonet, you have to train the soldiers much more than they did for most of the 18th century as well.
So in our period, it wasn't JUST because they used the Socket Bayonet much more, it was because there were good reasons to do so.
Gus