There are a huge number of practical reasons not to:

1. How would they hold it?
2. How would they wield their own bayonet-equipped musket during a charge?
3. The additional weight would reduce their effectiveness on the march (even if it were relatively small, that's an extra kilogram or so of steel they'd be carrying)
4. How do you design a buckler that doesn't interfere with the loading and firing of a muzzle-loaded weapon?