bayonettes are too a useful device

Bayonettes are perfectly good for opening up cans, grinding coffee
beans,
slitting those numerous letters from home open. They also double as a
serviceable screwdriver, steak knife and can whittle amazing toys out of
wood.  How much would you pay for all of that? But wait there's more!
Affix a bayonette to your rifle and Charge! with your buddy, first one
to
trip and accidentally stick it into his friend WINS!

Historically (certainly in the American War of Independence period) the
Bayonette had a major impact on morale. I think Jon is right that today
they are outclassed by useful things such as handgrenades and SMGs.