They did actually use shields according to Dorothy Perkins's book, The Samurai of Japan, during the sixth century.
However, a few hundred years later, when they began using bows and later, firearms.....hand-held shields became impractical.
So they instead latched large pieces of armour on their body and also used floor mounted mantlets.
Tahra might remember me asking for dimensions of our playmo cowboy saloon floor boards. I had been trying to customize some mantlets for my samurai klickies using just playmo parts with perhaps our playmo easel stands.
I even bought many of those playmo camera arms to try out but again, they didn't work
.....so, finally, sigh.....these...although much much better BUT not with playmo parts....
well, my samuai klickies can't complain